Elektra, Sai Assassin

Ninjutsu {3}{r}{r} ({3}{r}{r}, Return an unblocked attacker you control to hand: Put this card onto
the battlefield from your hand tapped and attacking.)
Power Up (Whenever this creature deals combat
damage to a player, if it does not have a +1/+1
counter on it, put a +1/+1 counter on it.)
Creatures you control with +1/+1 counters on
them have double strike.