1) Thundercloud procs can stack so that you don't have to push your rotation back and disrupt your timing instead saving them for your Umbral Ice phase.

2) Fire IV can proc Firestarter. This allows for a higher chance to use Fire III as your Astral Fire refresh, allows for an instant cast to stop GCD clipping, and helps with movement.

3) Freeze now grants Umbral Ice III when used.

4) Flare grants a proc for Freeze that allows it to be cast for 0 MP and instantly.

6) Umbral Hearts make the MP cost of Fire spells 0 and/or make it so that Fire spells also have the cast time they would in Umbral Ice.

I agree with other people saying Scathe cost reduced to 0 and Leylines becoming Between the Lines when Leylines is up.