Symphony, the Codebreaker

Hexproof
Defender
Symphony's Defender cannot be bypassed.
Whenever an attacking or defending creature dies from damage inflicted by Codebreakers you control, return it to the battlefield under your control, it is a Codebreaker in addition to its other types, and it gains "If this creature were to leave the battlefield, exile it instead."
Whenever a Codebreaker under your control dies or is exiled, add {e}{e}, and Symphony perpetually gains +1/+0.
If Symphony leaves the battlefield, you lose the game.