When you have Thunder III, you can leave Thunder II off. You will need to keep Thunder (1) for slowcasting.


Umbral Ice on AoE pulls:
Lv12 - Lv34: Blizzard II (50 potency/target) is more damage than Blizzard (180 potency) if there are at least four targets (200 potency total).
Lv35 - Lv49: Freeze (100 potency/target) is more damage than Blizzard if there are at least two targets.
Lv50 - Lv60: After Flare, Transpose and immediately begin casting Fire III, followed by Fire II, Fire II, Flare, Transpose, repeat. There is no ice. Unless a SCH or AST sneakily hastes you during your Flare cast, in which case you might have to insert a Freeze before Fire III so that you're slow enough to get MP for your fire spells.


At 60, on single targets, Blizzard isn't entirely useless, but its use is basically to recover from screw ups. You might be fighting a new mob and lose a Blizzard III because it jumped or went INVULNERABLE during your cast, or you might not be prepared for required movement. In either case you'll have very little MP and no Fire to transpose out of, and Blizzard will save you the further embarassment of sitting there doing nothing for several ticks while you wait for enough MP to Blizzard III.


The hard limit on Virus users is two because of Antibody. By the time the second Antibody wears off, the first user's Virus has cooled down.


Lethargy is useful on adds in some boss fights, and will make dealing with keepaway mechanics easier (e.g., slimes | Amon, Dread Knights | caged player, hearts | A7 boss).


Aetherial Manipulation is one of your "Additional Effects: Ignores mechanics." buttons.

/ac (Aetherial Manipulation) <mo>
/ac (Aetherial Manipulation) <t>
/ac (Aetherial Manipulation) <tt>
/ac (Aetherial Manipulation) <2>
/ac (Aetherial Manipulation) <3>
/ac (Aetherial Manipulation) <4>
/ac (Aetherial Manipulation) <5>
/ac (Aetherial Manipulation) <6>
/ac (Aetherial Manipulation) <7>
/ac (Aetherial Manipulation) <8>
/micon (Aetherial Manipulation)

Keep that macro on your bar somewhere near your Sprint button. You'll use it more as you become more comfortable with the timings of bosses' action scripts.