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Changeling (This card is every creature type.)
{X}: Until end of turn, creatures you control have base power and toughness X/X and gain all creature types.
Activating the ability with X = 0 will cause all creatures you control to become 0/0 and be put into the graveyard.
Changeling applies in all zones, not just the battlefield.
Mirror Entity's ability overwrites any effects that previously set a creature's base power and/or toughness. Any existing effects or counters that raise or lower a creature's power and/or toughness continue to apply to the creature's newly-set power and toughness.
