The Terraria Old Ones Army event is a tower defense crossover inspired by Dungeon Defenders II that punishes unprepared players. Spanning three distinct tiers tied to your world progression, it shifts focus from dodging single bosses to managing overwhelming crowd control and defending the fragile Eternia Crystal. If you don't build a proper arena, utilize sentries, and balance single-target burst with area damage, the waves will quickly break you.
Success requires treating this event like a specialized logistical puzzle rather than a standard boss fight. You need a flat surface, precise positioning for your Tavernkeep sentries, and a loadout tailored to each wave's specific mix of ground crushers and flying nuisances.
Understanding the Three Tiers and Progression
The event scales drastically as you progress through. Each tier introduces nastier enemies, higher health pools, and stricter DPS checks. Knowing what triggers each tier helps you time your attempts when your gear can actually handle the spike.
- Tier 1: Unlocks after defeating any world evil boss (Eater of Worlds or Brain of Cthulhu). It features 5 waves culminating in the Dark Mage mini-boss. Enemies have low health, making it an easy introduction if you've got molten or shadow armor.
- Tier 2: Unlocks after defeating any mechanical boss (The Destroyer, The Twins, or Skeletron Prime). Spanning 7 waves, it introduces the Ogre and flying threats like Drakins and Kobold Gliders. Crowd control becomes mandatory here.
- Tier 3: Unlocks after defeating Golem. This is the ultimate endgame challenge. It features 7 brutal waves ending with Betsy, a flying dragon boss that inflicts heavy damage and high knockback.
Arena Design and Sentry Placement
You can't just fight anywhere. The event spawns two mysterious portals on opposite sides of the Eternia Crystal. Enemies target the crystal directly, ignoring you unless you stand in their path.
Build a completely flat arena that spans at least 150 blocks in both directions from the crystal. If obstacles block enemy paths, they phase through them, rendering walls useless. Line the floor with Asphalt Blocks to maximize your running speed during Tier 2 and Tier 3.
Sentries are non-negotiable. Even in single-class playthroughs, you must use Etherian Mana dropped by slain enemies to place and maintain sentries.
- Place Lightning Aura sentries right where enemies cluster near the portals or the crystal base for consistent area-of-effect damage.
- Build a low ceiling or platforms about 20 blocks above the crystal to mount Ballista or Flameburst towers. This protects your base from exploding Kobold Gliders and helps shred flying targets like Wyverns and Etherian Lightning Bugs.
Wave Strategies for Hard Fights
Each phase of the event demands a shift in tactics. Getting tunnel vision on a mini-boss while ignoring minor mobs will cost you the crystal.
Dealing with Tier 2 and the Ogre
Wave 7 introduces the Ogre, a massive brute that swings a giant club and hurls slow-inducing slimeballs. Do not approach the Ogre in melee range unless you enjoy losing half your health bar to a single ground slam. Keep your distance, use piercing weapons or ranged guns, and let your sentries handle the smaller goblins while you whittle down the Ogre's health.
Surviving Tier 3 and Defeating Betsy
Betsy is the main hurdle in Tier 3. She alternates between swooping across the arena, raining fireballs that inflict the On Fire! debuff, and hovering to summon more waves.
- Stay mobile on your asphalt runway.
- When Betsy takes flight to breathe fire across the ground, use high-mobility wings to maneuver above her or take cover beneath your raised platform ceiling.
- Bring weapons with high single-target DPS paired with homing capabilities (such as Chlorophyte Bullets for Rangers or the Terra Blade for Melee users) to track her while dodging incoming fire.
Essential Gear and Loadouts
Maximizing your output means prioritizing offensive stats over defensive stacking. If you don't kill enemies fast enough, their sheer numbers will overwhelm the crystal's health pool.
- Melee: Weapons with wide arcs and heavy pierce, like the Night's Edge in pre-hardmade or the Terra Blade and Daybreak later on, clear out dense clusters of ground units instantly.
- Ranger: High-velocity guns paired with explosive or holy arrows provide incredible crowd clearing. Shroomite Armor's stealth bonus lets you stand still and pump out massive sustained damage during mid-waves.
- Mage: Magical harps, Nebula Blaze, or piercing spell books create zones of absolute destruction around the portals.
- Summoner: Tavernkeep armor sets (like Red Riding or Valhalla Gothic) are custom-made for this event because they directly boost both your summon count and your sentry capacity.
For official game mechanics, item drops, and weapon stats, you can reference the Terraria Wiki.
Frequently Asked Questions
Can I place banners during the Old Ones Army event?
No. Once you place the Eternia Crystal, you receive the Creative Shock debuff, which prevents you from placing or removing banners. You must set up any helpful banners nearby before you ever trigger the event.
What are Defender Medals used for?
Defender Medals are the unique currency dropped by mini-bosses and wave clears during the event. You spend them to purchase Tavernkeep armor sets, sentry canes, and special weapons from the Tavernkeep NPC.
Do enemies damage the player or just the crystal?
Enemies attack both. While their primary objective is the Eternia Crystal, they will aggressively attack you if you get in their way. Dying doesn't automatically fail the event, but it leaves the crystal entirely undefended while you respawn.
Is multiplayer easier for the Old Ones Army?
Yes. Splitting responsibilities—such as having one player hold down the left portal and another manage the right portal while sharing mana drops—makes managing the later waves significantly more manageable.
