Gollum can't block.
When Gollum enters, exile up to one target card from an opponent's graveyard. Each opponent loses 2 life.
{2}, Sacrifice an artifact or creature: Return this card from your graveyard to your hand. Activate only as a sorcery.
You don't have to choose a target for Gollum's second ability. However, if you do and that target becomes illegal by the time the ability tries to resolve, it will not resolve. Each opponent will not lose 2 life.