Can you react to "when I move"?

Yes, you can react to a "When I move" triggered ability.

According to the RiftJudge FAQ #5749 provided in the context, "When I move" is a triggered ability that is placed on the chain, which creates a window of opportunity for an opponent to play a Reaction spell or effect.

Understanding the Timing

The reason you can react to this specific ability involves how the game handles movement and triggers:

1. Movement is Instantaneous: According to Rule 441.3, the act of moving itself is instantaneous and does not use the chain. You cannot react to the movement itself, and it does not create a priority window.
2. Triggered Abilities use the Chain: However, per Rule 383.3, when a "When I move" trigger condition is met, that ability is placed on the chain.
3. Closed State: Once the triggered ability is added to the chain, the game state becomes "Closed." During a closed state, players have priority and may play Reaction cards in response to the item on the chain (see Rule 813.1.c.1 and the Showdown Flow guidelines).

Sequence of Events

If a unit moves and triggers a "When I move" ability:

1. Movement: The unit moves from its origin to its destination.
2. Trigger: The "When I move" ability triggers and is placed on the chain as a pending item.
3. Reaction Window: The chain is now "Closed." Players receive priority and may play [Reaction] cards to the chain.
4. Resolution: Once all players pass, the chain resolves in LIFO (Last-In, First-Out) order, resolving the reaction(s) first, followed by the "When I move" ability.

This is my interpretation based on the interaction between Rule 441.3 (movement does not use the chain) and Rule 383.3 (triggered abilities use the chain), supported by RiftJudge FAQ #5749 and RiftJudge FAQ #3814. No official FAQ exists that contradicts this interpretation.