Old One's Army

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Desktop only.png Desktop-Only Content: This information (or parts of it) 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. 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 if the player dies.

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. The 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 enter a ghost-like state wherein they can phase through any blocks obstructing their path to the Crystal.

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.

Arena requirements[edit | edit source]

The minimum distance required at each side to start the event is 61 blocks, measured from the center of the stand, however the portals will spawn further away given the space, up to 120 blocks away, and a minimum of 10 blocks between the floor and the ceiling (if there is one). If this distance requirement is not met, the Crystal will not be placed successfully, and a status message appears informing the player that the surface is inadequate.

You can build up to a height of three blocks before the blocks are considered as obstructing the necessary space.

Platforms and Actuated blocks that you go through when moving over will not count as flat space, but blocks with actuators on them that are solid will count and can be actuated after the event has started.

Anti-cheat mechanisms[edit | edit source]

To discourage complex arenas:

  • The Creative Shock debuff prevents placing or mining blocks during the event. It also prevents using buckets to add or remove liquids.
  • Blocks: Old One's Army monsters are able to go to a "ghostly" state where they go through blocks. They start in that state when they spawn, and they will go back to it if at any point there are no direct passage between them and you. For example, if you go to a tunnel below the arena, they will fall through the blocks to invade the tunnel. (This method can actually be exploited to make them unable to damage the crystal.)
  • Teleporter.png Teleporter: the invaders are not affected by teleporters, so you cannot use such mechanisms to prevent them from moving towards the crystal.
  • Lava.png Lava: the invaders take no damage from lava.
  • Dart Trap.png Traps: they work; however they are less efficient than sentries, and in fact traps will make the sentries less effective (since traps give invincibility frames to the monsters when they hit them, while sentries don't). Traps can still be used to soften up enemies a bit, but they should only be used in areas out of reach of sentries. It's generally better to place sentries all along the enemies' path and ignore traps altogether.

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 monsters simply going through, but it is possible to protect the crystal from projectiles this way.
  • Ice Rod.png Ice Rod can place temporary ice.
  • Sandgun.png Sandgun can place sand.
  • Explosives can destroy blocks.
  • Hoiks can be used to some extent to fling Etherian Mana your way; however, due to the way the game works you can only hoik Etherian Mana to the right. It's also not entirely effective as the between-wave timer usually allows you enough time to pick it all up anyway. But: they can also be used to hoik the crystal itself. if you make a hoik-loop where the crystal circles around, then it's pretty much invincible. However, this is most likely considered cheating from most players.
  • Conveyor Belt.png Conveyor Belts Desktop only.png can also be used to transport Etherian Mana towards the center, and unlike hoiks they work in both directions.
  • Dirt Rod.png Dirt Rods Can be used but mainly for dirt arenas. You can move the dirt to allow more obstacles for the enemies, even while the event is still going on.

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 a mini-boss in the final wave. Tier 1 happens when the event is triggered before any Mechanical Bosses have been defeated in Hardmode. The final wave will not end until a Dark Mage is defeated, which will then finish the event. Completing Tier 1 awards 5 Defender Medals in total.
  • Tier 2 consists of seven waves, with one or more Ogres serving as a mini-boss in the final wave. The Dark Mage will not appear in this tier. Tier 2 happens when the event is triggered in Hardmode worlds after at least one Mechanical Boss has been defeated. The final wave will not end until an Ogre is defeated, which will then complete the event. 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 happens when the event is triggered after the Golem has been defeated. Tier 3 is won as soon as 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 bosses, the regular enemies also differ with each invasion Tier, with stronger statistics and a more menacing appearance as higher tiers are unlocked.

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.

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 Shock Desktop only.png
Debuff tooltip You have lost the power of Creation!
Item (Quantity) Rate
Defender Medal.png Defender Medal Desktop only.png
• Amount depends on wave
100%
Old One's Army
Characters Unique Drops

Structures

Mysterious Portal.png Mysterious Portal Desktop only.png

Pre-Mechanical Boss:

Etherian Goblin.png Etherian Goblin Desktop only.png
Etherian Goblin Bomber.png Etherian Goblin Bomber Desktop only.png
Etherian Javelin Thrower.png Etherian Javelin Thrower Desktop only.png
Etherian Wyvern.png Etherian Wyvern Desktop only.png
Dark Mage.png Dark Mage Desktop only.png
Old One's Skeleton.png Old One's Skeleton Desktop only.png
(From Dark Mage)

After Killing One Mechanical Boss:

Kobold.png Kobold Desktop only.png
Drakin.png Drakin Desktop only.png
Kobold Glider.png Kobold Glider Desktop only.png
Wither Beast.png Wither Beast Desktop only.png
Ogre.png Ogre Desktop only.png

Post-Golem:

Etherian Lightning Bug.png Etherian Lightning Bug Desktop only.png
Betsy.png Betsy Desktop only.png

From all:

Etherian Mana.png Etherian Mana Desktop only.png

Banners:

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

From Dark Mage:

War Table.png War Table Desktop only.png
War Table Banner.png War Table Banner Desktop only.png
Dragon Egg.png Dragon Egg Desktop only.png
Gato Egg.png Gato Egg Desktop only.png
Dark Mage Mask.png Dark Mage Mask Desktop only.png
Dark Mage Trophy.png Dark Mage Trophy Desktop only.png

From Ogre:

Apprentice's Scarf.png Apprentice's Scarf Desktop only.png
Squire's Shield.png Squire's Shield Desktop only.png
Huntress's Buckler.png Huntress's Buckler Desktop only.png
Monk's Belt.png Monk's Belt Desktop only.png
Tome of Infinite Wisdom.png Tome of Infinite Wisdom Desktop only.png
Phantom Phoenix.png Phantom Phoenix Desktop only.png
Brand of the Inferno.png Brand of the Inferno Desktop only.png
Sleepy Octopod.png Sleepy Octopod Desktop only.png
Ghastly Glaive.png Ghastly Glaive Desktop only.png
Creeper Egg.png Creeper Egg Desktop only.png
Ogre Mask.png Ogre Mask Desktop only.png
Ogre Trophy.png Ogre Trophy Desktop only.png

From Betsy:

Flying Dragon.png Flying Dragon Desktop only.png
Sky Dragon's Fury.png Sky Dragon's Fury Desktop only.png
Aerial Bane.png Aerial Bane Desktop only.png
Betsy's Wrath.png Betsy's Wrath Desktop only.png
Betsy's Wings.png Betsy's Wings Desktop only.png
Betsy Mask.png Betsy Mask Desktop only.png
Betsy Trophy.png Betsy Trophy Desktop only.png
Treasure Bag (Betsy).png Treasure Bag (Betsy) Desktop only.png
During Expert Mode

From Eternia Crystal (NPC):

Defender Medal.png Defender Medal Desktop only.png

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 Goblin Desktop only.png
Etherian Goblin Bomber.png Etherian Goblin Bomber Desktop only.png
Etherian Javelin Thrower.png Etherian Javelin Thrower Desktop only.png
Etherian Wyvern.png Etherian Wyvern Desktop only.png
Dark Mage.png Dark Mage Desktop only.png
Kobold.png Kobold Desktop only.png
Etherian Lightning Bug.png Etherian Lightning Bug Desktop only.png
Drakin.png Drakin Desktop only.png
Kobold Glider.png Kobold Glider Desktop only.png
Wither Beast.png Wither Beast Desktop only.png
Ogre.png Ogre Desktop only.png
Betsy.png Betsy Desktop only.png
Defender Medal.png Defender Medal Desktop only.png 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 Flameburst Rod.png Flameburst Cane.png Flameburst Staff.png
Flameburst
Apprentice armor.png Apprentice Desktop only.png Dark Artist armor.png Dark Artist Desktop only.png Tome of Infinite Wisdom.png Tome of Infinite Wisdom Desktop only.png Betsy's Wrath.png Betsy's Wrath Desktop only.png Apprentice's Scarf.png Apprentice's Scarf Desktop only.png
Huntress Explosive Trap Rod.png Explosive Trap Cane.png Explosive Trap Staff.png
Explosive Trap
Huntress armor.png Huntress Desktop only.png Red Riding armor.png Red Riding Desktop only.png Phantom Phoenix.png Phantom Phoenix Desktop only.png Aerial Bane.png Aerial Bane Desktop only.png Huntress's Buckler.png Huntress's Buckler Desktop only.png
Monk Lightning Aura Rod.png Lightning Aura Cane.png Lightning Aura Staff.png
Lightning Aura
Monk armor.png Monk Desktop only.png Shinobi Infiltrator armor.png Shinobi Infiltrator Desktop only.png Sleepy Octopod.png Sleepy Octopod Desktop only.png /Ghastly Glaive.png Ghastly Glaive Desktop only.png Sky Dragon's Fury.png Sky Dragon's Fury Desktop only.png Monk's Belt.png Monk's Belt Desktop only.png
Squire Ballista Rod.png Ballista Cane.png Ballista Staff.png
Ballista
Squire armor.png Squire Desktop only.png Valhalla Knight armor.png Valhalla Knight Desktop only.png Brand of the Inferno.png Brand of the Inferno Desktop only.png Flying Dragon.png Flying Dragon Desktop only.png Squire's Shield.png Squire's Shield Desktop only.png

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.

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.

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]

  • 1.3.4.1: Hotfixes to bugs regarding the invasion.
  • 1.3.4: Introduced.
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