$0.01 @ TCGplayer
Slipstream Serpent can't attack unless defending player controls an Island.
When you control no Islands, sacrifice Slipstream Serpent.
Morph {5}{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.)
If a creature attacks a planeswalker, that planeswalker’s controller is the defending player.
Slipstream Serpent’s first ability applies only while you’re declaring attackers. If it attacks while face down and then is turned face up, it’s still attacking even if the defending player controls no Islands.
