Bouncy Boulder

It is a boulder that forgot how to stop. Cut the support out and it falls, then it keeps hopping along the ground for a while instead of rolling to a halt, hurting anything it clips on the way. The arc is closer to a bouncy bomb than to a rock, only faster.

That makes it worse than a plain boulder for a trap you want to aim and better for one you do not. If the corridor is narrow it will keep coming back for a second and third pass. In an open cave it goes wherever it likes, which is a problem when you are the one standing there.

Mine one inside a tight two-by-two pocket and the projectile hangs in place for a moment before it breaks, where the ordinary version pops immediately. That extra beat is enough to step out of the way, so wall one in before you touch it.

Natural spawns are rare in a normal world. If you want a supply, the special world seeds carry far more of them.