So the group I'm with just finished the tower with Katiyana. We are a NG Master Summoner of Desna with Summon Good Monster, Sacred Slayer Inquisitor of Shizuru, and a Mysterious Stranger 1/Ninja X. We were level 8 during this encounter. My summoner had 3 hound archons summoned from previous encounters in the tower (2 just from the remorhaz on the floor below).
Summoner: Dimension Door all three party members to ledge with Katiyana.
Ninja: 3 Focused Aim sneak attack shots, 91 damage
Sacred Slayer: Bane outsider(native), free action study target on hit w/sneak attack, 45 damage. Katiyana dead before acting.
We didn't even play out the combat with the 3 hound archons vs the hoar frost spirits as it would have been a joke at this point.
There's not a real point to this story, I just thought it was pretty fun to one round a CR 11 encounter when down 1 PC and wanted to share.