When Kog'Maw's Deathknell effect triggers, does Wielder of Water's Defender ability (from Discipline) still protect it, or has combat ended and the ability no longer applies?

Ruling: Deathknell effects resolve after combat has resolved, so Wielder of Water is no longer attacking or defending when the Deathknell damage occurs. Therefore, its Defender ability does not apply and it can be killed by the Deathknell effect.

Sequence:

• Combat resolves and damage is dealt
• Combat ends
• Deathknell effects trigger and resolve
• At this point, Wielder of Water is not in combat, so its "while attacking or defending" ability is inactive

Nuances:

• The cleanup phase that removes combat-long effects happens after combat ends, before Deathknell resolves
• Abilities that only work "while attacking or defending" only apply during a Showdown (combat)