Can you Starcross Rift Herald as it's moving to a battlefield to negate its move ability?
To answer your question, we must look at how movement and triggered abilities interact with the chain.
The Short Answer
No, you cannot use Star-Crossed to negate the Rift Herald's move itself, but you can react to the triggered ability that occurs after it arrives at the battlefield.
The Reasoning
- Movement is not on the Chain: Moving a unit from one location to another (whether by a Standard Move or a card effect) is a game action that happens immediately. It does not use the chain, so there is no window to "react" to the movement itself once it begins.
- Triggered Ability: The Rift Herald's ability ("When I move to a battlefield...") is a triggered ability. According to the <chain_rules>, triggered abilities are placed on the chain after the unit enters the new battlefield.
- The Timing Window:
- Rift Herald moves to the battlefield. The battlefield becomes occupied.
- The "When I move" trigger is placed on the chain. This creates a Closed State.
- Because the state is now Closed, you have the opportunity to play Star-Crossed as a [Reaction].
- Targeting and Resolution: You can play Star-Crossed targeting the Rift Herald and one of your own units. If Star-Crossed resolves first, it will return the Rift Herald to its owner's hand.
- As established in RiftJudge FAQ #11149 (regarding similar trigger interactions), if the source of a triggered ability (the Rift Herald) is removed from the battlefield before the ability resolves, the ability will whiff (do nothing) because it can no longer resolve its instructions relative to the battlefield where it moved.
Summary
You cannot stop the Rift Herald from moving to the battlefield. However, you can wait for its triggered ability to go on the chain, then use Star-Crossed to return the Rift Herald to its owner's hand. This effectively prevents the Rift Herald's triggered ability from resolving.
This is my interpretation based on the mechanics of triggered abilities and chain interaction. No official FAQ exists for this specific interaction, but it follows the established rules for ability resolution.