Buy @ TCGplayer
Whenever another creature you control enters, put a +1/+1 counter on this creature.
As long as this creature has three or more +1/+1 counters on it, it has flying and is a Knight in addition to its other types.
If Skyknight Squire enters at the same time as one or more other creatures you control, its first ability will trigger for each of those other creatures.
Once Skyknight Squire has been blocked, putting enough +1/+1 counters on it to give it flying won't cause it to become unblocked.
