The Yellow Materia is an enemy that appears in Crisis Core -Final Fantasy VII-.
This enemy boasts high Vitality and Spirit stats.
Zack should use a combination of Command Materia and Fire-based attacks to defeat the Yellow Materia. This foe drops tufts of Phoenix Down when defeated in the Cage of Binding, but only if Zack does not already have these in his inventory.
Materia means "matter" or "substance" in Latin. It also means "subject" in Italian and Spanish, and is the ascendant of Portuguese "Matéria".