How do you handle triggered abilities with illegal targets when they resolve?

Ruling: Triggered abilities with illegal targets follow the same rules as spells. When a triggered ability resolves, if any of its targets are no longer legal, those targets are unaffected by the ability as it resolves.

Sequence:

• A triggered ability behaves like an activated ability when placed on the chain
• Activated abilities follow the same process as playing cards
• The rules for handling illegal and impossible instructions apply to both spells and abilities
• You do as much as you can, replacing every instance of information of the now illegal target with NULL

Nuances:

• A target becomes illegal if it no longer meets the initial requirements before resolution (e.g., a unit at battlefield becomes an illegal target if it stops being at a battlefield before the ability that targeted it resolves)