Shrewd Hatchling enters the battlefield with four -1/-1 counters on it.
: Target creature can't block Shrewd Hatchling this turn.
Whenever you cast a blue spell, remove a -1/-1 counter from Shrewd Hatchling.
Whenever you cast a red spell, remove a -1/-1 counter from Shrewd Hatchling.
8/1/2008 If you cast a spell that’s both of the listed colors, both abilities will trigger. You’ll remove a total of two -1/-1 counters from the Hatchling.
8/1/2008 If there are no -1/-1 counters on it when the triggered ability resolves, the ability does nothing. There is no penalty for not being able to remove a counter.