顺便疯狂地享受了一把连它主人都没有过的后宫之乐。 Context MC's pet (male) broke into a cage that was filled with female animals. Thanks
顺便 - conveniently / along the way 疯狂地 - wildly 享受了 - enjoyed 一把 - an experience 连它主人 - that even it's master 都没有过的 - has never experienced before 后宫之乐 - pleasures of the harem Basically, the pet had a lot of wild sex.
(it/Pet's name) took the opportunity to enjoy a level of decadence that even his master never experienced. Rather than describe it graphically (wild sex), I think the intent is pretty clear here. I'm presuming it's already made clear that the cage is filled with female animals, so there's no need to repeat that.