Arcane Cloak x ManaStorm

Arcane cloak: "Spends x% of current mana"

ManaStorm: "When you Cast a Spell, Sacrifice all Mana to gain Added Maximum Lightning Damage"


So what happens when i cast arcane cloak having a manastorm unique shield?

Youll spend X% of current mana.

Then youll sacrifice all mana left to get the buff.

They are both separate things.

To use the lv20 gem info, you will use 64% of your mana for Arcane Cloak, then will sacrifice the 36% that is left for the buff from the shield.