Necrogen Censer

A self-contained clock with a hard ceiling: it enters carrying two charge counters, and each tap spends one to cost a player two life, so the entire structure is exactly four life lost across two activations on your own schedule. That cap is the whole design. You are not buying a recurring engine; you are buying a finite resource that exhausts itself in two taps, with no way past the ceiling short of adding counters. Two choices keep it modest. The ability targets a player and reduces life directly, which means it cannot touch creatures or planeswalkers and gives the opponent nothing to block or trade with. And the output is metered to the counters it enters with, so without proliferate or some other counter-adder it simply runs dry. The trade it offers is inevitability for patience: nothing the opponent does stops the bleed except destroying the artifact, and it ticks on your timeline rather than the board's. The trouble is that four life across two taps rarely keeps pace with what three mana buys in pressure or removal, which is why it reads cleaner in the abstract than it plays. The one genuinely structural wrinkle is that ammunition living on charge counters quietly invites builds that refill or proliferate them, stretching a deliberately capped artifact past what the printed text promises.