If a card in a player's graveyard has {X} in its mana cost, X is 0 for the purpose of determining its mana value.

If Driver of the Dead dies at the same time as a creature with mana value 2 or less, you can target that card and return it to the battlefield.

If a creature card with mana value 2 or less becomes a copy of Driver of the Dead and dies, it can be the target of its own ability.