jeeeeez Betty stole Gaster's attack to use againts him AND stole his dead son's theme song, at this point she's just making it as painful as possible for Gaster also the man who has nothing else to lose: origin
It's not very creative. If you can just steal someone's attack it's common sense to use the stealing attack power when your opponent is using their strongest attack
Guys, if you don't know, Neutral Animatios and I will make the OST. Yeah, its weird that the animator makes the OST, but ¯\_(ツ)_/¯. Anyway, she just uploaded a video. Go to see it!! Here's the link: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Zfbgo1VShds.html