clockwork steed enters the battlefield with four +1/+0 counters on it.

clockwork steed can't be blocked by artifact creatures.

at end of combat, if clockwork steed attacked or blocked this combat, remove a +1/+0 counter from it.

x, t: 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 this ability only during your upkeep.