Old One's Army

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Pc only.png Desktop-Only Content: This information (or parts of it) applies only to the desktop version of Terraria.
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.

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. 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.

Players are inflicted with the Creative Shock debuff for the duration of the event, which prevents the removal or placement of blocks and furniture during the entire event. However, actuated blocks can still be triggered.

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


Mysterious Portal.png Mysterious Portal

Pre-Mechanical Boss:

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

After Killing One Mechanical Boss:

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


Etherian Lightning Bug.png Etherian Lightning Bug
Betsy.png Betsy

From all:

Etherian Mana.png Etherian Mana


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

From Dark Mage:

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

From Ogre:

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

From Betsy:

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

From Eternia Crystal (NPC):

Defender Medal.png Defender Medal

Wave chart[edit | edit source]

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

Notes[edit | edit source]

  • The Eternia Crystal regenerates its health very slowly when not taking damage.
  • 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.
  • 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 two 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 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
  • Enemies can be blocked from reaching the Eternia Crystal using a Sandgun even when under the effects of Creative Shock.
  • 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.
  • If you use the Clinger Staff it can act a barrier and combined with a single Lighting Aura it can take down one side of the Old mans army till 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]

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