How does Fox Fire work when selecting targets and their might values change before resolution?

Ruling: Fox Fire targets are selected when the spell is cast and locked in at that point. On resolution, you kill as many of those locked-in targets as possible up to a total of 4 might, adjusting for any might changes that occurred.

Sequence:

• Select targets when casting the spell (total might must be 4 or less at this point)
• Targets are locked in
• On resolution, kill as many of the locked targets as possible up to 4 total might
• If a target's might increased but is still 4 or less, you can still kill it along with other targets totaling 4 might
• If a target's might increased above 4, you cannot kill it but kill the remaining valid targets

Nuances:

• Spells in Riftbound don't fizzle; you do as much as you can with the locked-in targets
• If you only selected one target and it gets buffed above 4 might, Fox Fire resolves killing nothing
• You cannot change or deselect targets after casting, even if might values change