Side note: I am 85 right now. I imagine the following changes as I get to 90.

Amplifier: Increases chances I get to Xenoglossy when I want to.
Paradox: Fire III, Fire IV x3, Paradox, Fire IV x3, Despair, Transpose, Xenoglossy(otherwise Paradox if no Polyglot), Blizzard IV, Thunder III, repeat

Fire III's potency is 260*1.8=468 for the second Fire III so Paradox at 500 unaspected is better to refresh duration of Astral Fire.

Fire IV's potency is still 310*1.8=558 which is higher than 500 so still should be trying to do as many Fire IV as possible.

Paradox's 0 mp cost makes it better than Blizzard IV to follow Despair, but still wanna cast it once for 3 Umbral Hearts.

Paradox also is a good alternative to Scathe due to it's 0 casting time when umbral ice (if need to move and triple cast is down). Transpose and then Paradox spam until you can stay still again.