If my opponent plays Mindsplitter, can I use Rebuke to return the unit back to their hand and does it stop the ability from going off?

No, you cannot use Rebuke to stop Mindsplitter's "When you play me" ability from triggering and resolving.

Here is the breakdown of why this interaction happens as it does:

1. Timing and The Chain

When your opponent plays Mindsplitter, the unit enters play and its "When you play me" triggered ability is placed on the chain. Because triggered abilities use the chain (as per <chain_rules>), the chain is now "closed."

• Rebuke is an [Action] spell. According to Rule 309.1.a and RiftJudge FAQ #3425, you cannot play [Action] spells while the chain is closed. You can only respond with [Reaction] cards.
• Even if you had a [Reaction] spell that could remove Mindsplitter from the board, it would not stop the ability.

2. Abilities on the Chain

According to Rule 359.3.e.5 and the general mechanics of the chain, once a triggered ability has been placed on the chain, it becomes an independent game object.

• Removing the source of the ability (Mindsplitter) from the battlefield does not remove the ability from the chain.
• The ability will continue to resolve normally even if the unit that created it is returned to the hand, destroyed, or otherwise moved.

Summary

• Can you Rebuke the unit? Only if the chain is open (e.g., if there were no other triggered abilities and your opponent passed priority to you after playing the unit). However, even if you did successfully Rebuke the unit, the "When you play me" ability is already sitting on the chain and will resolve regardless.
• Does it stop the ability? No. Triggered abilities resolve independently of their source.

This is my interpretation based on standard timing and chain rules. No official FAQ exists for this specific combination, but the interaction is consistent with how triggered abilities and the chain function in Riftbound.