The target instant or sorcery spell can have other targets as long as one of them is you.

If the spell mastery ability applies, you’ll create a copy of the instant or sorcery spell only if Psychic Rebuttal counters that spell. If that spell can’t be countered by spells or abilities, you won’t get a copy.

If Psychic Rebuttal creates a copy of the spell, 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.

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).

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.

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

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 a player sacrifices a 3/3 creature to cast Fling, and you copy it, the copy of Fling will also deal 3 damage to its target.

If the copy says that it affects “you,” it affects the controller of the copy, not the controller of the original spell. Similarly, if the copy says that it affects an “opponent,” it affects an opponent of the copy’s controller, not an opponent of the original spell’s controller.

Check to see if there are two or more instant and/or sorcery cards in your graveyard as the spell resolves to determine whether the spell mastery ability applies. The spell itself won’t count because it’s still on the stack as you make this check.