Are there currently any counters to Mindsplitter's ability?

No, there is currently no way to "counter" the "When you play me" ability of Mindsplitter.

According to the rules and official RiftJudge FAQs (specifically #9909, #10625, and #9017), here is the breakdown of why this is the case:

1. You cannot "Counter" the ability

There is currently no mechanic or card in the game that functions as an "ability counter." While you can use Defy to counter a spell, Mindsplitter’s ability is a triggered ability, not a spell. Per Rule 425.1 and RiftJudge FAQ #9909, Defy cannot target it.

2. You cannot stop it by removing the unit

Because triggered abilities that use the chain become independent game objects once placed there, removing Mindsplitter from the battlefield (e.g., using Rebuke or another removal spell) does not stop the ability from resolving. As established in RiftJudge FAQ #10874, the ability will continue to resolve normally regardless of what happens to the Mindsplitter unit itself.

3. What you can do

While you cannot "counter" or stop the ability, you can react to it once it has been placed on the chain. Because the ability uses the chain, it creates a "Closed State," allowing you to play [Reaction] speed spells or abilities (RiftJudge FAQ #10625).

• Example: You could use Star-Crossed as a reaction. While this won't stop the ability from resolving, it could allow you to return the targeted unit to your hand before the ability forces you to discard it, or otherwise manipulate the board state in response to the trigger.

In summary, there is no way to negate or prevent the execution of Mindsplitter's triggered ability once it has been placed on the chain.