Mystical Reversal on a repeated spell?

Yes, if you use Mystic Reversal to steal a spell that has had its Repeat cost paid, you gain control of the entire spell, including all instances of the repeat effect.

According to the FAQ regarding repeat spells and Mystic Reversal:

• When you gain control of a repeat spell, the repeated spell effects are part of the original spell which has been finalized and paid for.
• Gaining control does not change the fact that the repeat cost has been paid.
• You receive one spell that performs its effects multiple times (e.g., twice if one repeat cost was paid, three times if two were paid).

Key points to remember:

• No new costs: You do not need to pay the repeat cost again; you inherit the spell as it was finalized by your opponent.
• New choices: As per the card text of Mystic Reversal, you may make new choices for the spell (such as new targets) when you take control of it.
• Playing the spell: While you gain control of the spell and its effects, the spell is still considered to have been "played" only once.

This is based on the official FAQ for Riftbound regarding Mystic Reversal and repeat effects.