TNT Barrel

It hits harder than anything else you can place and leaves the terrain completely alone, so you can detonate one inside a build without cratering it. Almost any contact sets it off: a stray pickaxe swing, a projectile that clipped it, an enemy attack that missed you. Treat it as live from the moment it leaves your hand, and never place one at melee range of where you plan to stand.

It is not a mechanism, so running a wire to the barrel itself does nothing. The trick is to wire the block underneath instead: actuate the floor away and the barrel breaks itself on the way down. That is the only clean way to build a triggered trap out of them, and it means your switch has to be somewhere the blast radius does not reach.

A world with that seed active generates these instead of the usual dart and boulder setups, and the temple gets packed with them. That flips temple diving from a slow, careful crawl into something closer to a minefield, where the danger is what you swing at rather than what you step on.