Generator Servant

{T}, Sacrifice this creature: Add {C}{C}. If that mana is spent on a creature spell, it gains haste until end of turn. (That creature can attack and {T} as soon as it comes under your control.)

The List

Ultimate Masters

{T}, Sacrifice Generator Servant: Add {C}{C}. If that mana is spent on a creature spell, it gains haste until end of turn.

Magic 2015

{T}, Sacrifice Generator Servant: Add {2} to your mana pool. If that mana is spent on a creature spell, it gains haste until end of turn. (That creature can attack and {T} as soon as it comes under your control.)

An instant or sorcery spell is not a creature spell, even if that spell creates creature tokens.

If a creature spell has generic mana only in its alternative or additional cost, the creature will still gain haste.

If the mana is spent on a noncreature spell that becomes a creature later in the turn, that creature won't have haste.

If the mana is spent on two different creature spells, each of those spells (and resulting creatures) will gain haste until end of turn.