Does Tryndamere's excess damage ability count damage from spells cast during a showdown, or only damage assigned during the combat damage step?

Ruling: Tryndamere only counts excess damage assigned during the combat damage step, not damage dealt by spells. Damage from spells is "dealt" but not "assigned" in the rules terminology.

Sequence:

• Spell damage dealt during showdown does not count toward Tryndamere's excess damage
• Only damage assigned during the combat damage step counts
• Spell damage can still factor in if it marks damage on a unit before combat damage assignment (e.g., 4 spell damage on a 5 might unit, then assigning 6 combat damage to it would count as excess)

Nuances:

• You must assign exactly lethal damage to all defending units before any excess damage counts (this is a known issue in the current rules document but the intention is confirmed)
• Against a 4 might and 1 might unit, you would need 10 total might to trigger Tryndamere's effect (5 to kill each unit, plus 5 excess)
• The rules for damage assignment are currently being rewritten, so some ambiguity exists in the current comprehensive rules