At first, you fight Orin's cat form. It's quite harmless. But it's very important that you get your deck's scaling online, because once Orin transforms, it will get very nasty. She has over 300 HP and is joined by four zombie fairies with 15 HP and 99 Flight (so effectively 30 HP each).

It's imperative that you kill off as many zombie fairies as you can on the very first turn they appear, otherwise they will start stacking massive amounts of Block on everyone - each other and Orin.

The reward for the fight is the Cat Cart, which is essentially another Lizard Tail. It revives you with more HP the earlier in Act III you find it - it charges up every floor. You also get gold and a card. It's like killing an elite.

Unless you're certain that you can kill off the fairies quickly, you should eat the curse in the event. This fight might be more deadly than the Act III boss. But it's like Lagavulin - you get a couple of turns to set up.

It's there entirely to kill your run if you forgot to turn it off and you're not playing Marisa. If you're playing Marisa then it's a test of "Does your deck have Fairy Destruction ray?"

I honestly find that it's way overtuned for a random event especially since the only safe way out is to eat a fairly destructive curse too. If only the option to Turn it off in the mod config didn't reset itself to default the event being on each time i restart the game...

I have to agree with the overtuning, even if I usually beat it. It just feels like BS to deal with as it's tougher than a lot of bosses are in my book.