Steel Immortal

If none of your opponents controls any creature, Steel Immortal gains Defender.
Empower (If this creature attacks or blocks, put a +1/+1 counter on it at the end of the turn)
Restoration 3 (If this creature is sent to the Graveyard, it stays on the battlefield and is tapped instead. Then put 3 sleep counters on this creature. During your untap phase, if this creature has Sleep counters on it, remove one of them and do not untap this creature)