Mizzix, Replica Rider — ruling 1

Any spell you cast will be copied if you pay the cost, not just one that requires targets.

Mizzix, Replica Rider — ruling 2

You may only pay the cost once, as the triggered ability resolves. You can't pay it more than once to get additional copies.

Mizzix, Replica Rider — ruling 3

If a copy is created, you control the copy. That copy is created on the stack, so it's not "cast." Abilities that trigger when a player casts a spell won't trigger. The copy will then resolve like a normal spell, after players get a chance to cast spells and activate abilities.

Mizzix, Replica Rider — ruling 4

The copy will have the same targets as the spell it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If, for one of the targets, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).

Mizzix, Replica Rider — ruling 5

If the copied spell is modal (that is, it says "Choose one –" or the like), the copy will have the same mode. You can't choose a different one.

Mizzix, Replica Rider — ruling 6

If the copied spell has an X whose value was determined as it was cast, the copy has the same value of X.

Mizzix, Replica Rider — ruling 7

You can't choose to pay any additional costs for the copy. However, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too. For example, if you sacrifice a 3/3 creature to cast Fling, and you copy it, the copy of Fling will also deal 3 damage to its target.

Mizzix, Replica Rider : règles, fonctionnement et interactions (MTG)

Mizzix, Replica Rider is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Flying Whenever you cast a spell from anywhere other than your hand, you may pay . If you do, copy that spell and you may choose new targets for the copy. If the copy is a permanent spell, it gains haste and "At the beginning of your end step, sacrifice this permanent." (A copy of a permanent spell becomes a token.)

How it works : Mizzix, Replica Rider

Original English text — Wizards of the Coast / Scryfall

#1December 2, 2022· Wizards of the Coast
Any spell you cast will be copied if you pay the cost, not just one that requires targets.
No other card is named in this ruling.
#2December 2, 2022· Wizards of the Coast
You may only pay the cost once, as the triggered ability resolves. You can't pay it more than once to get additional copies.
No other card is named in this ruling.
#3December 2, 2022· Wizards of the Coast
If a copy is created, you control the copy. That copy is created on the stack, so it's not "cast." Abilities that trigger when a player casts a spell won't trigger. The copy will then resolve like a normal spell, after players get a chance to cast spells and activate abilities.
Card named in this ruling
Copy
#4December 2, 2022· Wizards of the Coast
The copy will have the same targets as the spell it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If, for one of the targets, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).
Card named in this ruling
Copy
#5December 2, 2022· Wizards of the Coast
If the copied spell is modal (that is, it says "Choose one –" or the like), the copy will have the same mode. You can't choose a different one.
Card named in this ruling
Copy
#6December 2, 2022· Wizards of the Coast
If the copied spell has an X whose value was determined as it was cast, the copy has the same value of X.
Card named in this ruling
Copy
#7December 2, 2022· Wizards of the Coast
You can't choose to pay any additional costs for the copy. However, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too. For example, if you sacrifice a 3/3 creature to cast Fling, and you copy it, the copy of Fling will also deal 3 damage to its target.
Card named in this ruling
Copy