Old One's Army Guide: All 3 Tiers, Medals & Betsy (1.4.5)

Old One's Army guide — Eternia Crystal terrain rules, the three tiers and mini-bosses, and the Defender Medal sentry gear worth grinding.

10/5/2026 1.4.5.8 Terraria Wiki Team 4 min read

FAQ

How do you start the Old One's Army?

Buy an Eternia Crystal and an Eternia Crystal Stand from the Tavernkeep, place the stand on flat ground, and press Open on it to socket the crystal. The Tavernkeep appears in the world as the Unconscious Man once the Eater of Worlds or Brain of Cthulhu is defeated.

What terrain does the Eternia Crystal need?

A 121-tile-wide flat clearing — 60 tiles each side of the stand — with at least 10 tiles of vertical space. Platforms and inactive blocks count against the 3-tile obstacle allowance, so fight it on a dedicated flat lane, not inside your base. Failure shows a status message instead of consuming the crystal.

What are the three Old One's Army tiers?

Tier 1 (post evil-boss): 5 waves ending in Dark Mages, pays 5 Defender Medals. Tier 2 (post mechanical boss): 7 waves ending in Ogres, pays 25 medals. Tier 3 (post-Golem): 7 waves with Dark Mages and Ogres plus Betsy as the final boss, pays 100 medals — Expert adds 30–49 more inside Betsy's treasure bag.

What is Etherian Mana used for?

Etherian Mana drops from event enemies and fuels the Tavernkeep's sentry summons — Flameburst, Explosive Trap, Lightning Aura, and Ballista towers. You start each event with 10 mana (one sentry), collect more to run several towers at once, and all unspent mana vanishes when the event ends.

Is the Old One's Army worth doing?

For summoners, absolutely — the Tavernkeep's sentries are among the strongest summon weapons of their tier, and Tier 3's Betsy drops endgame loot like the Betsy's Wrath, Flying Dragon, and Aerial Bane. Clearing one event also permanently unlocks sentry use in normal play for that world.

What is the Old One’s Army?

The Old One’s Army is Terraria’s official crossover with Dungeon Defenders 2 — a tower-defense event where waves of Etherian enemies pour out of twin portals and march on an Eternia Crystal you’re defending. If the crystal dies, the event ends; clear every wave and you’re paid in Defender Medals, a special currency spent with the Tavernkeep.

Unlike every other invasion, the Old One’s Army doesn’t care about your world spawn point — you build the arena yourself by choosing where the crystal stands.

How do you summon it?

Defeat the Eater of Worlds or Brain of Cthulhu — the Tavernkeep then starts spawning as the Unconscious Man somewhere in the world (surface or underground; he’ll be lying on the ground) — our bound NPC rescue guide has the full search strategy.
Buy an Eternia Crystal and Eternia Crystal Stand from him — both cost ordinary coins.
Place the stand and press Open to socket the crystal.

Terrain is the catch: the stand needs 60 clear tiles on each side (a 121-tile lane centered on the stand) and 10 tiles of vertical space. Building more than 3 tiles up counts as obstruction — platforms too. Portals spawn up to 120 tiles out on each side if given room, so a long flat lane buys you maximum defense distance. During the event you cannot place or break blocks — anti-cheat rules baked into the mode.

The three tiers

Tier	Unlock	Waves	Final mini-boss	Medal payout
1	Eater of Worlds / Brain of Cthulhu dead	5	Dark Mage	5 medals
2	Any mechanical boss dead (Hardmode)	7	Ogre	25 medals
3	Golem dead	7	Dark Mages + Ogres in mid waves, Betsy finale	100 medals (+30–49 in Expert via her Treasure Bag)

There’s a 30-second breather between waves — press Open on the stand to skip it.

Defender Medals and the sentry economy

Defender Medals buy the Tavernkeep’s real prize: four sentry families — Flameburst (fire towers), Explosive Trap, Lightning Aura, and Ballista — each in Rod/Cane/Staff grades. During the event they run on Etherian Mana (dropped by enemies; you start with 10, enough for one tower), and stacking mana lets multiple sentries stay deployed permanently until the event ends.

Once you’ve cleared the event in a world, those sentries work outside it under normal summon rules — turning them into real summon builds. The armor sets on the same vendor buff a matching sentry type further. Event enemies drop no coins, biome keys, or seasonal loot — everything of value comes from the medal loop and mini-boss drops (weapons, pets, vanity, trophies at 1/10 and masks at 1/7).

Practical tips

Build the arena ahead of time: a flat 121+ tile lane with a ceiling of at least 10 tiles, campfires, and heart lanterns along the path.
Sentries on the lane edges — portals can spawn up to 120 tiles away, so spread towers across the approach rather than stacking them at the crystal.
Farm Tier 1 repeatedly for early Defender Medals — 5 medals per ~5-wave clear is slow, but the gear buys you into Tier 2 which pays 5× as much.
Betsy is a real boss — she hovers, fires flame rings, and hits like a truck; come in post-Golem gear, not post-Destroyer gear. Our boss order page shows where she slots in progression.

Screenshot sources: cover — official Steam store screenshot (Re-Logic); gallery — wiki.gg Eternia Crystal asset.