Try to draw something unique background and try and error with paint tool sai and ps. God, I failed the reflections... And the aurora not so realistic.. But at least my bae Asriel looks HOT. Hope you like it.

Undertale by Toby Fox
Fanart by meh
Tutorial --> http://jocarra.deviantart.com/art/Fantasy-Aurora-Borealis-Tutorial-316862233
Reference --> https://i.ytimg.com/vi/1kKkRtVlwrM/maxresdefault.jpg