Like in Mulley's example, Celes' Runic combined with other characters' shields would be neat. It'd cool if she could temporarily enchant an ally's shield, letting them us it to reflect or absorb one magic spell.

Hmm... Gau learns Rages, which are monster attacks. Strago learns Blue Magic spells, which are monster magic. By combining the two, Gau could temporarily carry the 'spirit' of a particular monster, gaining all its strength, magic and abilities for one battle. That'd be kind of cool, since the 'berserk' nature of the Rage attacks is sometimes an inconvenience.