Cannot be blocked by artifact creatures.When Clockwork Steed comes into play, put four +1/+0 counters on it. At the end of any combat in which Clockwork Steed attacked or blocked, remove one of these counters.X, T: Put X +1/+0 counters on Clockwork Steed. You may have no more than four of these counters on Clockwork Steed. Use this ability only during your upkeep.