Spreading Plague

Pure punishment dressed as a board state. The destruction keys off the entering creature's color rather than its controller, and it spares nothing that shares that color, so committing a creature to the battlefield signs a death warrant for half the table. That symmetry is the whole design tension: the effect is devastating precisely because nobody, its controller included, can develop creatures into it without consequence. The deck this wants is one that does not care to play creatures at all, or one built to exploit the color clause: cast a creature in a color you have otherwise abandoned, watch the opponent's developed board evaporate, and leave your own off-color stragglers standing. It also rewards manipulating a creature's color, since the trigger asks only what colors are shared. Forbidding regeneration closes the obvious escape valve of an era when regeneration shields were a standard answer to mass removal, but the more important thing is that this is a stax-flavored hate piece, not a one-time sweeper: it does not clear the board once, it keeps the board clear, taxing every future creature anyone casts as long as the enchantment survives. The cost to the pilot is real, and that cost is the point; this is removal you build a whole strategy around, not a card you slot in alongside a normal creature curve.