If a unit has damage marked on it from one spell (Void Seeker), and then another spell (Stupefy) reduces its Might so that the previously marked damage becomes lethal, does this count as 'killing a unit with a spell' for Immortal Phoenix's ability?

Ruling: Under current rules, Stupefy reducing a unit's Might to make previously marked damage lethal is unlikely to trigger Immortal Phoenix. The official position is that this interaction is unclear in current rules and will be clarified in the upcoming Core Rules update.

Sequence:

• Void Seeker deals 4 damage to a 5 Might unit (damage is marked but unit survives)
• Stupefy reduces the unit's Might by 1 (now 4 Might with 4 damage marked)
• During cleanup, the unit is killed by state-based actions

Nuances:

• If you react to Void Seeker with Stupefy before Void Seeker resolves, Stupefy resolves first (reducing Might to 4), then Void Seeker deals 4 damage and kills the unit, which would trigger Phoenix
• Under current rules, technically nothing "kills" units except cleanup/state-based actions, making Phoenix's trigger condition unclear
• Some interpret that cleanup actions can be considered effects of what caused the cleanup ("vibes-based" ruling), which would allow Stupefy to trigger Phoenix
• The rules currently don't track damage sources or use "last known information" for permanents
• An official response indicated this interaction is "unlikely" to work but awaits Core Rules clarification