Clockwork Steed

Clockwork Steed enters with four +1/+0 counters on it.<br>Clockwork Steed can't be blocked by artifact creatures.<br>At end of combat, if Clockwork Steed attacked or blocked this combat, remove a +1/+0 counter from it.<br>, : Put up to X +1/+0 counters on Clockwork Steed. This ability can't cause the total number of +1/+0 counters on Clockwork Steed to be greater than four. Activate only during your upkeep.