Then immediately here, because I'd like to know if this is a glitch, Please don't let it be one. Thanks for your time, and if it is, then I hope I've helped you out.
I recreated this. If it's used in that battle, it's a 2-pip spell and does the regular damage. If it's not used in that battle, it becomes a 5-pip spell, as it should be, and it does the same damage. This is a bug, and it's being submitted to Support.
I was ecstatic at first because I thought it was only mutating with vampire, but after seeing that it also works on ghoul, I was disappointed.
Yea, It's definitely game breaking, and should be fixed immediately. I've used it in practice PvP, but I wouldn't dare use it elsewhere, as it truly is unbalanced. Quite frankly, it ruins the game, but hopefully it will get fixed soon.
I'd also like to thank the development team, keep up the good work. This game has come a long way in a short time.