Is the Madame of Mystery Archvillain bugged?
The Madame of Mystery Archvillain has extremely high resistances to all damage except Toxic, before factoring in any level and rank modifiers that occur due the Purple Patch. Psionic damage is 15% effective (85% resistance). Smashing, Fire, Cold, Energy, and Negative Energy is 35% effective (65% resistance). Lethal is 55% effective (45% resistance), and Toxic is not resisted at all. On top of that, she has Archvillain-level regen, so many players think that she has incredible base regen, when the reality is her resistances factoring in. Powers that debuff damage resistance (Sonic Siphon, for example) and regeneration rate (Transfusion, for example) are key to defeating her if you cannot outright out-damage her resistances plus regeneration rate. Keep in mind though, that these powers will be resisted fairly heavily in and of themselves, so will be much less effective than when used on a normal foe.
