Old One's Army

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Desktop version Desktop-Only Content: This information applies only to the Desktop version of Terraria.
BiomeBannerOldOne'sArmy.png
Old One's Army Icon.png
Progress bar icon

Betsy Trophy.png "The old one's army is approaching!" Betsy Trophy.png

The Old One's Army is a unique Dungeon Defenders 2 crossover event that can be triggered by placing an Eternia Crystal on the Eternia Crystal Stand. There are three versions (Tiers) of the event, the second and third of which are triggered by defeating a Mechanical Boss and Golem respectively.

Once the Eternia Crystal is placed, and after a 5-second countdown, the objective is to protect the Eternia Crystal NPC from waves of enemies seeking to destroy it. If the Crystal is destroyed, the event terminates. If it is kept "alive" until all waves are cleared, the event is defeated.

This event makes use of a unique currency called Defender Medals, which are dropped by the Eternia Crystal after its later waves are cleared. Defender Medals are used to purchase special corresponding weapons and armor from the Tavernkeep NPC.

This event can be exceptionally difficult, not only due to the toughness of its enemies, but because of the various anti-cheat/exploit methods it employs. The terrain requirements for summoning the event, and the Creative Shock debuff, prevent most of the usual arena tricks. Event enemies are not moved by Teleporters, and they don't take damage from Lava. Even if one manages to circumvent the Creative Shock debuff by using items like the Ice Rod to place blocks, enemies can enter a ghost-like state wherein they can phase through any blocks obstructing their path.

Summoning[edit | edit source]

An Eternia Crystal Stand must be placed, and then an Eternia Crystal must be placed on it by right-clicking the stand with a Crystal in the player's inventory. Both the Crystal and its Stand are purchased from the Tavernkeep NPC for coins. The Tavernkeep can be found randomly in a world after the Eater of Worlds or the Brain of Cthulhu has been defeated.

Terrain requirements[edit | edit source]

Summoning this event has some unique requirements for the terrain around the summon area. If they are not fulfilled, the Eternia Crystal cannot be placed successfully, and a status message appears informing the player that the surface is inadequate.

  • A minimum clearing of 61 tiles horizontally is required on each side of the Eternia Crystal Stand, measured from the center of the Stand (a 123-tile clearing in total, with the Stand at the center tile). The enemy portals will spawn further away if given the space however, up to 120 tiles away from the center of the Stand on each side.
  • A minimum clearing of 10 tiles vertically is required (ie. between the "floor" and the "ceiling," if there is one).

You can build up to a height of three tiles before blocks are considered obstructing the necessary space. Platforms and Actuated blocks that players and enemies can move through cannot count as part of a flat floor, and will count against the three-tile height allowance; but floor blocks with Actuators on them that are solid when the Crystal is placed will count as flat, and can be successfully actuated after the event has started.

Anti-cheat mechanisms[edit | edit source]

  • The Creative Shock debuff prevents placing or mining blocks during the event. It also prevents using Buckets to spill or collect any liquids.
  • All Blocks: Blocks cannot be used to completely prevent event enemies from advancing. Old One's Army enemies are able to go to enter a "ghostly" state where they can move through blocks. They initially spawn in this state, then re-enter it whenever there is no clear path between them and the player. For example, if the player enters a tunnel below the arena, enemies will fall through the blocks to enter the tunnel.
  • Teleporter.png Teleporter: Event enemies are not affected by Teleporters, so Teleporters cannot be used to prevent them from moving towards the Crystal.
  • Lava.png Lava: Event enemies take no damage from Lava.
  • Dart Trap.png Traps: Traps will damage event enemies normally, but less efficiently than sentries; Traps can additionally make sentries less effective, since trap attacks cause invincibility frames in the enemies they hit, while sentries don't. Traps may still be useful in areas out of the reach of sentries.

Things that are still possible:

  • Actuator.png Actuators can be used to transform the arena after the event has started. Keep in mind that walls can result in the enemies simply moving through, but this can help protect the Crystal from projectiles.
  • Ice Rod.png Ice Rod can place temporary ice blocks.
  • Sandgun.png Sandgun can produce Sand.
  • Explosives can destroy blocks.
  • Conveyor Belt.png Conveyor BeltsDesktop Version can be used to move Etherian Mana towards the player.
  • Dirt Rod.png Dirt Rods can be used to move Dirt Blocks in the area and create obstacles for enemies.

Waves[edit | edit source]

The event consists of a set number of waves, with each wave becoming progressively more difficult (see wave chart). At the end of each wave, there is a 30-second countdown to the next wave, signified by a timer appearing over the Eternia Crystal.

The event comes in three possible tiers, depending on game progression when the event is triggered:

  • Tier 1 consists of five waves, with one or more Dark Mages serving as mini-bosses in the final wave. Tier 1 is triggered when the event is summoned before any Mechanical Bosses have been defeated in Hardmode. The final wave ends when one Dark Mage is defeated. Completing Tier 1 awards 5 Defender Medals in total.
  • Tier 2 consists of seven waves, with one or more Ogres serving as mini-bosses in the final wave. Dark Mages will not appear in this tier. Tier 2 is triggered when the event is summoned in a Hardmode world after at least one Mechanical Boss has been defeated. The final wave ends when one Ogre is defeated. Completing Tier 2 awards 25 Defender Medals in total.
  • Tier 3 consists of seven waves, with the boss Betsy spawning in the final wave. The Dark Mage and Ogre will also spawn during the previous three waves. Tier 3 is triggered when the event is summoned after the Golem has been defeated. The final wave ends when Betsy is defeated. Completing Tier 3 awards 100 Defender Medals in total. In Expert mode worlds, an additional bonus of 30-49 Defender Medals is dropped by Betsy's Treasure Bag.

In addition to the difference in bosses, the common event enemies also differ between Tiers, with stronger statistics and a more menacing appearance in higher tiers.

Defender Medals and Sentries[edit | edit source]

The completion of each wave, beginning with the third, awards the player Defender Medals, a special currency used to purchase items from the Tavernkeep NPC that can help players defeat future Old One's Armies. Among them are special sentry summon weapons, which are fueled by Etherian Mana, a resource that drops only during this event. Etherian Mana allows multiple sentry minions to remain placed simultaneously and permanently until the event is over, with more Etherian Mana allowing more sentries to be placed. All Etherian Mana disappears once the event is over, whether uncollected or within the player's inventory.

At the beginning of the event, the player will receive 10 Etherian Mana, allowing them to place one sentry. Note that sentries not obtained from the Tavernkeep (such as the Queen Spider Staff) do not and cannot use Etherian Mana, but can be summoned separately.

Each sentry type available from the Tavernkeep (Flameburst, Explosive Trap, Lightning Aura, Ballista) comes in three different tiers: Rod, Cane, and Staff, with the Staff being the most expensive and the most powerful.

Before the event is completed successfully at least once, the Tavernkeep's sentry weapons will only function during the Old One's Army event, and will not function outside of it. Once the event is completed successfully in a world, the weapons can then be used outside the event.

Drops[edit | edit source]

Each boss and mini-boss in the event has a trophy (10% chance) and a mask (14.29% chance). Betsy also drops a Treasure Bag in Expert mode only (100% chance).

Several enemies also drop pets, vanity items, and powerful weapons and accessories. All enemy banners dropped during this event are non-functional, and do not provide the player with any of the usual defense or damage boosts that other enemy banners provide.

Enemies will not drop biome-specific drops, such as Biome Keys, or coins, even when wearing the Lucky Coin or its derivatives. They also do not drop Presents during Christmas, nor Goodie Bags during Halloween.

Content[edit | edit source]

Eternia Crystal (NPC)
Eternia Crystal (NPC).png
Statistics
Type Background object
Max Life T1: 1000
T2: 3000
T3: 5000
Defense T1: 14
T2: 18
T3: 45
Inflicts debuff Creative Shock.png Creative ShockDesktop Version
Debuff tooltip You have lost the power of Creation!
Item (Quantity) Rate
Defender Medal.png
Defender Medal Desktop Version
• Amount depends on wave
100%
Old One's Army
Characters Unique Drops

Structures

Mysterious Portal.png Mysterious PortalDesktop Version

Pre-Mechanical Boss:

Etherian Goblin.png Etherian GoblinDesktop Version
Etherian Goblin Bomber.png Etherian Goblin BomberDesktop Version
Etherian Javelin Thrower.png Etherian Javelin ThrowerDesktop Version
Etherian Wyvern.png Etherian WyvernDesktop Version
Dark Mage.png Dark MageDesktop Version
Old One's Skeleton.png

After Killing One Mechanical Boss:

Kobold.png KoboldDesktop Version
Drakin.png DrakinDesktop Version
Kobold Glider.png Kobold GliderDesktop Version
Wither Beast.png Wither BeastDesktop Version
Ogre.png OgreDesktop Version

Post-Golem:

Etherian Lightning Bug.png Etherian Lightning BugDesktop Version
Betsy.png BetsyDesktop Version

From all:

Etherian Mana.png Etherian ManaDesktop Version

Banners:

Etherian Goblin Banner.png Etherian Goblin BannerDesktop Version
Etherian Goblin Bomber Banner.png Etherian Goblin Bomber BannerDesktop Version
Etherian Javelin Thrower Banner.png Etherian Javelin Thrower BannerDesktop Version
Kobold Banner.png Kobold BannerDesktop Version
Etherian Lightning Bug Banner.png Etherian Lightning Bug BannerDesktop Version
Drakin Banner.png Drakin BannerDesktop Version
Etherian Wyvern Banner.png Etherian Wyvern BannerDesktop Version
Kobold Glider Banner.png Kobold Glider BannerDesktop Version
Wither Beast Banner.png Wither Beast Banner
Old One's Skeleton Banner.png Old One's Skeleton BannerDesktop Version

From Dark Mage:

War Table.png War TableDesktop Version
War Table Banner.png War Table BannerDesktop Version
Dragon Egg.png Dragon EggDesktop Version
Gato Egg.png Gato EggDesktop Version
Dark Mage Mask.png Dark Mage MaskDesktop Version
Dark Mage Trophy.png Dark Mage TrophyDesktop Version

From Ogre:

Apprentice's Scarf.png Apprentice's ScarfDesktop Version
Squire's Shield.png Squire's ShieldDesktop Version
Huntress's Buckler.png Huntress's BucklerDesktop Version
Monk's Belt.png Monk's BeltDesktop Version
Tome of Infinite Wisdom.png Tome of Infinite WisdomDesktop Version
Phantom Phoenix.png Phantom PhoenixDesktop Version
Brand of the Inferno.png Brand of the InfernoDesktop Version
Sleepy Octopod.png Sleepy OctopodDesktop Version
Ghastly Glaive.png Ghastly GlaiveDesktop Version
Creeper Egg.png Creeper EggDesktop Version
Ogre Mask.png Ogre MaskDesktop Version
Ogre Trophy.png Ogre TrophyDesktop Version

From Betsy:

Flying Dragon.png Flying DragonDesktop Version
Sky Dragon's Fury.png Sky Dragon's FuryDesktop Version
Aerial Bane.png Aerial BaneDesktop Version
Betsy's Wrath.png Betsy's WrathDesktop Version
Betsy's Wings.png Betsy's WingsDesktop Version
Betsy Mask.png Betsy MaskDesktop Version
Betsy Trophy.png Betsy TrophyDesktop Version
Treasure Bag (Betsy).png

From Eternia Crystal (NPC):

Defender Medal.png Defender MedalDesktop Version

Wave chart[edit | edit source]

Key
Pre-Mechanical Boss (T1) After Killing One Mechanical Boss (T2) Post-Golem (T3)
Enemy Wave 1 Wave 2 Wave 3 Wave 4 Wave 5 Wave 6 Wave 7
Etherian Goblin.png Etherian GoblinDesktop Version
Etherian Goblin Bomber.png Etherian Goblin BomberDesktop Version
Etherian Javelin Thrower.png Etherian Javelin ThrowerDesktop Version
Etherian Wyvern.png Etherian WyvernDesktop Version
Dark Mage.png Dark MageDesktop Version
Kobold.png KoboldDesktop Version
Etherian Lightning Bug.png Etherian Lightning BugDesktop Version
Drakin.png DrakinDesktop Version
Kobold Glider.png Kobold GliderDesktop Version
Wither Beast.png Wither BeastDesktop Version
Ogre.png OgreDesktop Version
Betsy.png BetsyDesktop Version
Defender Medal.png Defender MedalDesktop Version Reward 1 1 1 1 3 3 3 11 6 25 15 60

Equipment chart[edit | edit source]

The Old One's Army event brings associated equipment. The armor and sentry weapons are available from the Tavernkeep in exchange for Defender Medals, while other weapons and accessories are dropped by event enemies.

Tier 2 items become available after one Mechanical Boss is defeated, and Tier 3 items become available after Golem is defeated.

Class Sentries Tier 2 Armor Tier 3 Armor Tier 2 Weapon Tier 3 Weapon Accessory
Apprentice

(magic)

Flameburst Rod.png Flameburst Cane.png Flameburst Staff.png
Flameburst
Apprentice armor.png ApprenticeDesktop Version Dark Artist armor.png Dark ArtistDesktop Version Tome of Infinite Wisdom.png Tome of Infinite WisdomDesktop Version Betsy's Wrath.png Betsy's WrathDesktop Version Apprentice's Scarf.png Apprentice's ScarfDesktop Version
Huntress

(ranged)

Explosive Trap Rod.png Explosive Trap Cane.png Explosive Trap Staff.png
Explosive Trap
Huntress armor.png HuntressDesktop Version Red Riding armor.png Red RidingDesktop Version Phantom Phoenix.png Phantom PhoenixDesktop Version Aerial Bane.png Aerial BaneDesktop Version Huntress's Buckler.png Huntress's BucklerDesktop Version
Monk

(light melee)

Lightning Aura Rod.png Lightning Aura Cane.png Lightning Aura Staff.png
Lightning Aura
Monk armor.png MonkDesktop Version Shinobi Infiltrator armor.png Shinobi InfiltratorDesktop Version Sleepy Octopod.png Sleepy OctopodDesktop Version /Ghastly Glaive.png Ghastly GlaiveDesktop Version Sky Dragon's Fury.png Sky Dragon's FuryDesktop Version Monk's Belt.png Monk's BeltDesktop Version
Squire

(tank melee)

Ballista Rod.png Ballista Cane.png Ballista Staff.png
Ballista
Squire armor.png SquireDesktop Version Valhalla Knight armor.png Valhalla KnightDesktop Version Brand of the Inferno.png Brand of the InfernoDesktop Version Flying Dragon.png Flying DragonDesktop Version Squire's Shield.png Squire's ShieldDesktop Version

Notes[edit | edit source]

  • The Eternia Crystal regenerates its health very slowly when not taking damage.
  • Bringing a Mechanical Boss summoning item to a pre-Hardmode world and vanquishing one will still only produce Tier 1 of the invasion.
  • Traps like Spiky Ball Traps or Super Dart Traps can do a small amount of damage to the Eternia Crystal.
  • At the start of the 7th wave at T3, Betsy will spawn off screen on the ground instead of the mysterious portals.
  • The event is considered cleared once the final boss of each Tier is defeated, regardless of how many enemies are left at that point. The "cleared" status is indicated by white light surrounding the Crystal, as well as a change in music, by which point the event is considered won even if enemies then proceed to touch the Crystal or the player dies. The event can even be won posthumously, if the remaining sentries finish off the last boss.

Tips[edit | edit source]

For more elaborate strategies on defeating Old One's Army, including Weapon and Arena recommendations, see Guide:Old One's Army strategies.

  • Because of the Creative Shock debuff, any building work to prepare the arena must be completed before. It is not possible to place or remove blocks or furniture while the event is happening, not even between waves.
  • If you are just starting a pre-mechanical boss world, and you have found the Tavernkeep, the first item you should buy is the Lightning Aura Rod, because if you place two lightning auras next to each portal, it is impossible for any enemy except the Dark Mage to get through the auras. Note that this only works in T1 (pre-Mechanical Boss).
  • If you are doing all 3 tiers of the event, it is recommended to save up 25 defender medals from doing Tier 1 before defeating a mechanical boss and moving to Tier 2. That way, you'll be able to buy a Tier 2 sentry summon weapon before attempting to do the Tier 2 version of the event. Attempting to defeat the Tier 2 event with only Tier 1 equipment puts you at a significant disadvantage. Saving up enough defender medals from Tier 2 to buy some Tier 3 gear once it becomes available is recommended for the same reason.
  • There are a few sentry summoning weapons not sold by the Tavernkeep: the Queen Spider Staff, the Staff of the Frost Hydra, the Rainbow Crystal Staff, and the Lunar Portal Staff. These are quite useful, because they use regular mana rather than Eternian mana, so using them enables you to have more sentries placed than would otherwise be possible. The Lunar Portal can also easily kill flying enemies, allowing you to focus on ground enemies. The armor sold by the Tavernkeep will increase how many of these sentries you can summon at one time.
  • If you are in a Hardmode world but have yet to defeat a mechanical boss, you can easily farm the event with a Blessed Apple or Ancient Horn mount. Simply run back and forth. The damage the mounts do while charging will one-hit kill all enemies besides the Dark Mage.
  • Endgame strategies: A maxed out Summoner with 11 Stardust Cell Staff minions and a Legendary Star Wrath can finish the event through wave 6 trivially. Wave 7 requires a lot of dodging, but the boss will probably die before it destroys the crystal. The S.D.M.G. with Luminite Bullets, or the Phantasm with Luminite Arrows, are also very useful. Other useful endgame items: Last Prism, Shadowbeam Staff, Snowman Cannon, Toxic Flask, Meowmere, Spore Sac, Staff of Earth, Scutlix mount
  • Keep the area above the lanes clear, as flying enemies will phase right through the ceiling anyway; blocks in the way only serve to make them unreachable by player attacks.
  • Players can use a one-block thick ceiling to their advantage, however, as it allows air enemies to be targeted by dedicated elevated towers, where they are more likely to score hits.
  • Platform blocks can support sentry summons, by using free-standing platforms, you can elevate your turrets without blocking off your own attacks.
  • If you use the Clinger Staff, it can act as a barrier. Combined with a single Lightning Aura sentry, it can take down one side of the army until around Wave 4.
  • The Nimbus Rod is extremely effective in Tier 1, as it kills all enemies in one hit except the Dark Mage. If you place the cloud towards the crystal-facing side of a pillar, no enemies will get through aside from the Dark Mage, which the player can handle. You will need to replace the cloud every so often, though.
  • If the player enters a tunnel below the arena, enemies will fall through the blocks to enter the tunnel; this behavior can be exploited to make them unable to damage the Crystal as they move themselves behind barriers to attack the player instead.
  • Hoiks can be used to some extent to fling Etherian Mana your way, however only to the right. This is of limited use since the break timer between waves offers plenty of time to gather Etherian Mana manually.
  • Hoiks can be used on the Eternia Crystal itself, and a hoik-loop can move the Crystal continuously so that it cannot be easily hit.

Trivia[edit | edit source]

  • If you look closely, the Eternia Crystal slowly develops cracks as it gets more damaged.

See also[edit | edit source]

History[edit | edit source]

Events
 
Random Events Rain • Slime RainDesktop VersionConsole Version • Blood Moon • SandstormDesktop Version • Solar Eclipse
Summonable Events Goblin Army • Frost Legion • Pirate Invasion • Solar Eclipse • Pumpkin Moon • Frost Moon • Martian MadnessDesktop VersionConsole Version • Lunar EventsDesktop VersionConsole Version • PartyDesktop Version • Old One's ArmyDesktop Version
Seasonal Events Valentine's DayMobile Version3DS version • St. Patrick's DayMobile Version • EasterMobile Version3DS version • OktoberfestMobile Version3DS version • ThanksgivingMobile Version3DS version • Halloween • Christmas
Unimplemented Events Chinese New YearMobile Version
Promotional Content