Clockwork Steed

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/blocked this combat, remove a +1/+0 counter from it.

[Variable Colorless], [Tap]: 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.