You may have Sakashima the Impostor enter as a copy of any creature on the battlefield, except its name is Sakashima the Impostor, it's legendary in addition to its other types, and it has ": Return Sakashima the Impostor to its owner's hand at the beginning of the next end step."
Sakashima leads a mono-blue clone/control deck that copies the best creature on any battlefield, then leverages flexibility, card advantage, and tempo to grind the table down. You stall early with counters and interaction, develop value engines, then assemble a copy-based combo or take over with overwhelming card advantage and tempo. The bounce ability lets you reset Sakashima to dodge removal or re-copy a juicier target.
Endlessly flexible commander that becomes whatever's best on the board, even your opponents' bombs
Bounce ability protects against targeted removal and lets you re-target a better creature
Mono-blue gives access to the best counterspells, card draw, and clone effects in the format
Synergizes with any powerful ETB or clone payoff already in your 99
Sakashima is mediocre on an empty board with no good creatures to copy
Mono-blue lacks efficient removal and struggles against go-wide tokens and resolved enchantments/artifacts
Vulnerable to board wipes since the deck leans on creatures and clones
Can be slow and reactive, ceding initiative to faster combo/aggro decks
A strong copy target and blink engine that abuses ETB clones for repeatable value.
Add the best blue cantrips and counters (Mystic Remora, Fierce Guardianship, Force of Will) plus fast mana like Mana Crypt and Sol Ring to lower your reactive curve. Lean into a tight clone-combo line—Spark Double or Phantasmal Image plus an infinite ETB or untapper—so Sakashima isn't just value but a wincon. Round out with strong copy targets in the 99 (Brago, Consecrated Sphinx, Urabrask-style payoffs) so there's always something worth becoming.