Gollum, Riddle Master

Legendary Creature — Halfling Horror

As Gollum enters, choose odd or even. (Zero is even.) Whenever an opponent casts a spell with mana value of the chosen quality, choose one that hasn't been chosen — • Put a +1/+1 counter on Gollum. • Each opponent loses 2 life and you gain 2 life. • Draw a card.