Chromeshell Crab

Mana cost: {4}{U}
Type: Creature — Crab Beast
Power / toughness: 3 / 3
Set: Commander 2011 #41 (rare)
Price: $0.35 USD

Morph {4}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When this creature is turned face up, you may exchange control of target creature you control and target creature an opponent controls.

Chromeshell Crab has 3 printings, first in Legions (2003). EDHREC ranks it #9,930 among Commander cards. It appears most in Kadena, Slinking Sorcerer decks (5,502 on EDHREC). 2 public decks on TCG run it. It has 5 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: not legal
pioneer: not legal
standard: not legal
brawl: not legal

Public decks that run Chromeshell Crab

Faceless Menace - Commander 2019, led by Kadena, Slinking Sorcerer
Political Puppets - Commander 2011, led by Zedruu the Greathearted

Commanders that run Chromeshell Crab most

Deck counts from EDHREC.

Often played with Chromeshell Crab

Cards that show up in the same decks on EDHREC.

Rulings

2004-10-04: The creatures can’t attack until you start a turn with them under your control. So you can’t swap and then attack.
2004-10-04: You choose the two target creatures when the triggered ability is put onto the stack. You do not have to choose Chromeshell Crab. You choose whether or not to do the exchange on resolution.
2004-10-04: The exchange fails if either you no longer control your creature or the other creature is now controlled by you.
2004-10-04: The exchange fails if either target is not still on the battlefield at that time.
2004-10-04: The trigger occurs when you use the Morph ability to turn the card face up, or when an effect turns it face up. It will not trigger on being revealed or on leaving the battlefield.