Maximized Acid Fog deals 360/360/120/180/120/180/90/72/60/60 and probably stays at that or is reduces to 30 after really long time.
Maximized Cloudkill deals 240/180/120/90/80/80/45/40/36/30/30 and stays at that number.
Maximized Evard's black Tentacles deals 360/360/180/180/120/120/90/72/60/60 and stays at that number.(they deal avg 25 physical damage, but everything resists/is immune to the physical damage part)
AoE's Damage is not only reduced way too much each time it hits, but a new spell doesn't deal its full damage it should.. If a monster was once hit by AoE, it won't take full damage from new/different AoE spell, but will only take the half of the last one unless its 60, it will further take only 60 damage.
I.e. before engaging Toad Demon in a fight, you cast one Max Acid Fog. It deals its damage, 360/360/180. You cast 2nd Max Acid Fog in different location, BUT it deals 180/120/120/90/72/60. Now you cast 3rd Max Acid Fog somewhere else and move with that toad there, but it only takes 60/60/60/60 damage. Doesn't matter if you cast Reg/Max/Emp AoE of the same name or not, they all share damage dealt.
It's like Melee character hitting a monster deals half the damage less each round or each time it successfully hits target. With the exception that a melee can hit monster few times a round, while AoE spell damages only once PER round.
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If a monster fails save on Evard's black tentacle , monster takes dealt 30 acid damage, while it deals 60 acid damage on successful save. Quite strange but i just saw it happen when testing it in caves of eternal life on magma lord. Wanted to make sure AoE spells work the way i described it here.
If a monster fails save on Inciendary Cloud, monster takes less than 10 damage. If monster successfully rolls
dice, it takes high damage. I don't know if failed saves count towards the damage countdown(don't know what should i call it).
wall of fire seems to work fine on failed save. takes 1/2 damage on successful save.