X-23, Deadly Weapon

A tribal payoff that grows itself and the newcomer in one motion: every Mutant that follows onto the battlefield takes a counter, and X-23 takes one too, so a chain of small bodies fattens in lockstep. The narrow creature type is what earns the rate. A version keyed to any "creature you control" at would snowball out of any green board; restricting the trigger to Mutants means the payoff only fires once a deck has committed to a specific tribe, and until then this is just a 3/3 body. The doubling structure is what makes the counters worth chasing: each Mutant arrival is a two-for-one investment in size, so a curve of cheap bodies can outsize individual fatties without spending a card on pump. The scaling is linear, not exponential: three Mutants entering at once produce the same six counters as three entering across three turns, so the card favors neither a slow drip nor an explosive turn. What it does favor is quantity of triggers, which rewards width over singular threats. And the counters live where they matter, distributed across the whole board rather than stacked on X-23 alone. That distribution is the real insurance: spot removal or a bounce spell that answers X-23 leaves every counter it handed out sitting on creatures that are still there, so the growth the card produced does not unwind when the engine itself is gone.