Moonshadow Ninjas

Moonshadow Ninjas costs {1} less to cast for each creature target opponent controls.
Switcharoo {2}{w} ({2}{w}{t}: Remove target attacking creature you don't control from combat and replace it with Moonshadow Ninjas. You still control it.)
Whenever Moonshadow Ninjas' Switcharoo cost is paid, this creature gets +3/+0 and double-strike until end of turn.