Siege Zombie

A drain engine whose only cost is tapping bodies, and the tension it creates is between board presence and reach. Assembling three untapped creatures pulls them out of the combat step, so each activation forces a choice: swing this turn, or peck opponents down from behind the lines. That pushes it toward token strategies where the fodder is disposable and the incremental drain stacks up faster than blockers can, black's go-wide plans in particular. The ability has no tap symbol of its own and no mana cost attached, so it fires as often as you can gather three ready creatures, and it slips past any interaction keyed on spending mana or on targeting: opponents lose life regardless. This is quiet inevitability, worthless in isolation and a genuine clock once the surrounding creatures arrive, a life-loss source that grows with headcount rather than with power or toughness. You run it for the button, not the 2/2 attached to it.