Shrewd Hatchling [Eventide]

Shrewd Hatchling enters the battlefield with four -1/-1 counters on it. {U/R}: 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.