Mimics don't need perfect disguises. They need only the perfect victims: the naive, the young, or the poor of sight.

Planechase

Battlegate Mimic

Whenever you cast a spell that's both red and white, Battlegate Mimic becomes 4/2 and gains first strike until end of turn.

Whenever you cast a spell that's both red and white, Battlegate Mimic has base power and toughness 4/2 until end of turn and gains first strike until end of turn.

Eventide

Whenever you play a spell that's both red and white, Battlegate Mimic becomes 4/2 and gains first strike until end of turn.