Explosive Trap Rod

The three tiers are bought from the Tavernkeep with Defender Medals. Killing any one mechanical boss puts the Explosive Trap Cane in his stock, and killing Golem adds the Explosive Trap Staff. Before any of them will function in the open world you have to clear an Old One's Army run at least once. The game notes that clear against both the world and the character, so a brand new character walking into a cleared world can use sentries there, and the character who did the clearing carries the permission with them wherever they go.

This is not a turret. You place it, it detonates whenever something comes near, and it survives its own blast to do it again until the timer expires or the event ends. The detection box sits well above the trap rather than centered on it, and that is the placement rule that matters: one on the floor reaches a long way up and barely at all downward. Set them on the ground beneath the lane enemies travel and they catch everything passing overhead, including things you never had line of sight on.

Huntress and Red Riding set bonuses change this sentry more than they change anything else. The cycle between explosions shortens sharply, halving again for the better of the two sets, and every detonation coats what it hits in Oiled, which makes fire damage bite harder. Three or four of them clustered at a spawn portal will erase an entire wave before it walks out of the blast area. Ogres are the exception and have the bulk to stroll through, so keep something pointed at them. For Etherian Wyverns, ring the Eternia Crystal with traps instead, since their dive brings them into range on the way in.

The trap throws off roughly torch level light, and you can summon one anywhere on screen and hold the button down. That makes it a decent spelunking aid: sweep the cursor across the dark and every detonation reveals a slice of cave. Starfury does the same job with the advantage that its projectile passes through tiles. Fabled is the modifier to aim for, though a heavily stacked summon build tips the top tier over to Ruthless. If you would rather have a Lightning Aura instead, shimmering one of these converts it to the matching tier.