Katarina, Hexakill, Abyssal

Howdy! I just got out of a hexakill game in which our katarina rolled face (real shocker), but she and I both found something that explains her success. Upon checking her items, her abyssal sceptre was reducing the MR of all nearby enemies by 93 and eventually 120-something in addition to all her other items. She got the coveted hexakill, praise be, but I can't help but feel bad about the circumstances. 2-shotting a tanky amumu is fun to watch, but frustrating i'm sure.