Cannot be blocked by walls.

When Clockwork Swarm comes into play, put four +1/+0 counters on it. At the end of any combat in which Clockwork Swarm attacked or blocked, remove one of these counters.

, : Put X +1/+0 counters on Clockwork Swarm. You may have no more than four of these counters on Clockwork Swarm. Use this ability only during your upkeep.