You was a Monster that could shape shift but maintaining your Tail and Red Ears, so you someday was Relaxing near a lake and out of nowhere you see a Mewnian Woman looking at you, you get scared and change your form randomly because she is the daughter of the current Queen of Mewni.

"Oh, sorry, I... Didn't wanted to scare you, I just found you very interesting..." She approaches to see if you're okay.