Kaza, Roil Chaser

Flying, haste
{T}: The next instant or sorcery spell you cast this turn costs {X} less to cast, where X is the number of Wizards you control as this ability resolves.

"What sort of life is that, huddling in the familiar and safe? No thanks. Put me right in the center of the action."

Outlaws of Thunder Junction Commander

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Zendikar Rising

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Kaza's cost reduction can reduce only generic mana in a spell's cost. It can't reduce colored mana requirements.

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Kaza's activated ability). The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.