Reflect-Null makes all magic cast buy that user ignore the Reflect status. It's useful if you want Dagger/Eiko to cast Curaga on a party with Auto-Reflect.

Mag Elem Nul makes all magic cast by the user non-elemental. It's pretty useless as it makes the -aga spells a weaker version of Flare. Doomsday with Mag Elem Nul is suicide.