Mirror-Mad Phantasm + Unstable Shapeshifter

Mirror-Mad Phantasm

Unstable Shapeshifter

How it works

1. Cast Mirror-Mad Phantasm by paying 3.
2. When Mirror-Mad Phantasm enters the battlefield, Unstable Shapeshifter triggers, causing Unstable Shapeshifter to become a copy of Mirror-Mad Phantasm until end of turn.
3. Activate Unstable Shapeshifter by paying 1, shuffling Unstable Shapeshifter into your library and milling your entire library due to it not having a card named Mirror-Mad Phantasm in it.

This clever interaction exploits a clever quirk in naming conventions to mill your entire library in one fell swoop. When you cast Mirror-Mad Phantasm, Unstable Shapeshifter enters the battlefield and transforms into a copy of it, inheriting its ability while retaining its own name. Because the copied creature's name is still Unstable Shapeshifter rather than Mirror-Mad Phantasm, activating that ability forces you to shuffle it away and reveal cards endlessly, failing to ever find a match with the correct name until your entire library is dumped straight into the graveyard.