The six Act I bosses share four abilities between them, so learning these counters prepares you for the stronger variants in Act II. What changes is the health pool and how little room for error you get.
The danger isn't the damage, it's the hole. If your whole defense sits in one pocket, losing a tower opens the lane. Cover every segment with at least two towers before this fight, even if both are cheap Archers. Redundancy beats power here.
It tries to cross your kill zone before you've done enough damage. Hold Frost Nova until the surge starts — casting early wastes it entirely. A Frost Mage or Cryo covering the back half is insurance if your timing slips.
Single-target builds drown here: your damage is locked on the boss while adds walk past. Bring at least one Mage or Bomb before this stage. Splash clears the adds without ever taking damage off the boss.
Damage poured into the shield is wasted. Stop casting when it goes up and let sustained tower fire wear it down instead. Save Meteor Strike for the moment it drops — burst into an unshielded boss is worth several times the same spell used early.
Same ability, far less forgiveness. One slow spell is no longer enough. Build layered kill zones — two separate pockets rather than one strong cluster — so the surge still passes through damage after clearing the first.
The final boss times its shell to blunt your strongest windows. Maximum single-target uptime wins this: upgraded Hunters with Sniper, plus a maxed Bomb. Enter with every spell available and spend them only in the gaps between shields.
From Endless wave 10, bosses arrive two at a time — and now escorted by a full horde rather than alone. Every cycle they get tougher.