Festercreep

A board sweeper that bills itself as a creature, then quietly turns its own body into ammunition. The 0/0 base printing means it would collapse instantly without the counter it enters with, so the counter is not a bonus: it is the creature's actual existence. Activating the mass-shrink effect costs you that existence one point at a time, because the price of pulling the trigger is removing a +1/+1 counter, and with only one counter that removal drops the toughness to zero. The ability itself never touches Festercreep (it reads "all other creatures"); what kills the Elemental is the activation cost, not the resolution. So a lone copy gives you exactly one symmetric -1/-1 pulse before the cost of firing it sends the body to the graveyard: a one-shot Shrivel stapled to something that gets in the way for a turn first, in the lineage of the cheap black mass-shrink effects that have always punished go-wide boards of small creatures. The whole calculus inverts the moment you bank extra counters. Each additional +1/+1 counter is another -1/-1 wave you can unleash without dying, and the body grows between pulses rather than withering toward zero. Feed it a counter-doubling or counter-adding engine and the modest attrition piece becomes a recurring death-fog that scales with how much fuel you can supply. The design rewards reading the counter not as a stat line but as a fuel gauge.