Yumcax magic damage?

On RDM with 90+111 INT, +101 Magic Attack, +55 Magic Accuracy, I was using every element at different times on Yumcax, every T1 was doing about 2 damage, T2s were 4, T3s were 7, T4s were 12. After using Elemental Seal with Burn, lowering Yumcax's INT, and using Impact, to lower it even further by a great deal, my damage went up to 4s, 9s, 17s, and 23s, these are not exact numbers, but they are not far off. Not a single nuke I did the entire battle did more than 50 damage, no matter the debuff, no matter the buff, no matter what I tried. I believe there is some sort of bug with this NM which is making it take much to little damage from any nukes, its stats are placed way to high, and even after the changes on the 6th I doubt anyone will be getting evaluations with these kind of numbers. Even if you take into account that the rate was at 37%, the -80% Damage taken, I should have been doing more than 200s on my highest tier with my gear.

Maybe it's DT is higher than 80% at that colo rate? Maybe it has mdb as well. Also based on other readings it seems to have decent magic evasion so might be some resists as well