Grave Peril

A standing trap parked face-up: the moment any nonblack creature enters, the enchantment sacrifices itself and takes that creature down with it. The trigger fires whenever a nonblack creature hits the battlefield, on any turn, including your own and including something flashed in at instant speed, and the destruction is mandatory once it resolves. That automaticity is both the appeal and the limit. It cannot be held for the right target, cannot leapfrog a chaff creature to hit the bomb behind it, and answers whatever lands first. The nonblack clause is the quiet color-pie tax: a mono-black opponent walks straight through, and even a black splash on the other side hands them an out. Where it earns its place is the cost structure. It sits on the board pre-paid, a one-for-one in card economy no different from holding up a kill spell, except spent in advance and visible to everyone. That visibility is the rub. It functions as much as a tax as a removal spell, making the opponent's first nonblack creature cost more than its mana, whether they pay by walking into it or by playing around it. And because the destruction goes on the stack like any other trigger, the opponent gets priority before it resolves: an instant-speed indestructibility grant, a flicker, or a bounce can negate it, the opponent spending one card to answer your one card, which is the even trade the trap was always going to be when they had the spare mana.