Deluge Virtuoso [SOS 042]

When this creature enters, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Opus — Whenever you cast an instant or sorcery spell, this creature gets +1/+1 until end of turn. If five or more mana was spent to cast that spell, this creature gets +2/+2 until end of turn instead.