Is Stealthy Pursuer's ability a triggered ability or a passive ability, and can it still resolve if the unit it's moving with (First Mate) is removed by Gust after the ability triggers?

Ruling: Stealthy Pursuer's ability is a passive ability that is worded like a trigger, not a true triggered ability. The units move together at the same time rather than sequentially.

Nuances:

• Despite being worded with "When" (which typically indicates a triggered ability), it functions as a passive ability
• The card may need errata to clarify its function
• If it were a true triggered ability, there would be a sequence where: (1) declare moving the unit, (2) Stealthy triggers, (3) opponent can react, and the original unit would still be at the first battlefield during this window