Spear Trap

Spear traps are Temple fixtures, which puts them behind Golem. You cannot mine them without a Picksaw and explosives will not free them early either. A few sometimes generate just outside the Temple door, and those are worth grabbing on your way in since they are the only ones you can take before the boss.

The spear runs a long way in a straight line, passes through every enemy on that line and retracts when it meets a wall. That makes it the trap of choice for the floor of a wide arena. Wire a row along the ground, hang the whole line off a single timer, and events like the Pumpkin Moon lose a lot of their pressure. A hammer rotates them, so a vertical bank covering the side of an arena works just as well.

Piercing projectiles hand out invincibility frames, and your own traps are not exempt from that. A wall of spears firing into a boss can end up blocking your weapon from connecting, so treat them as crowd control rather than as damage you are counting on. Actuators let you switch a bank off when you want it out of the way.