Fusion Summon 1 Fusion Monster from your Extra Deck, by banishing Fusion Materials listed on it from your GY face-down, but it cannot attack this turn.
The main feature of Necro Fusion is it’s ability to Fusion Summon using monsters in the graveyard. Here are some other cards capable of achieving the same feat but are locked to specific archetypes. If your deck is of a specific archetype It would be better to use it’s in-archetype fusion card.
Future Fusion lets you put fusion materials from your deck to the graveyard. Use Necro Fusion and banish those fusion materials to summon your Fusion monster quicker. If Future Fusion also succeeds after 2 turns you will have 2 copies of the Fusion monster on the field.