I’ll use the formulas in game to help explain:
Damage = Damage Taken
Resist = All Spell Resist
Resist = Resist * ( Infusion Rank * 0.05 )
Damage = Damage - ( Damage * ( Resist / ( Resist + (Enemy Level*100) ) ) )
This resulting Damage is then taken away from whatever your Mana Pool is.
As far as working for Skyfall, TnT, other world effects, we have a few bugs that might be bypassing mana shield that we’re looking into.