Mizzix of the Izmagnus

Mizzix's last ability doesn't change the mana cost or mana value of any spell. It changes only the total cost you pay.

Experience counters are the second kind of counters a player can have, joining poison.

If there are additional costs to cast a spell, or if the cost to cast a spell is increased by an effect (such as the one created by Thalia, Guardian of Thraben's ability), apply those increases before applying cost reductions.

All experience counters are identical, no matter how you got them. For example, the last ability will count experience counters that you got from the first ability, from another ability, from proliferating, and so on.

If an instant or sorcery spell you cast has {X} in its mana cost, you choose the value of X before calculating the spell's total cost. For example, if that spell's mana cost is {X}{R} and you have one experience counter, you could choose 5 as the value of X and pay {4}{R} to cast the spell.

The cost reduction can apply to alternative costs such as flashback costs.