Buni is not an Angel. He looks like one, because he feels like it lol.
His power comes from the control that he took from the player by tricking them. He already didn't have a soul from the beginning of the story (very long backstory that I don't feel like yapping bout here). So that plus all of the control of his own game world gave him a god complex.
He toyed with his own Home for a little while. Mixing and matching personalities. Seeing how far he could push programs. But due to his nature, he got bored pretty fast.
So he went out for the first time, and to have some enrichment activities to do. He decided to use his powers to grant people their wish.
And of course, its with a price that, you have to do one thing Buni requests. Its often not something for himself, being that he doesnt feel emotions that much, making anything that could be given to him useless.
But if there's one thing that entertains him the most, it's a good story, and what better way to do that than to be the reason of the conflict. Or create one.
He usually makes wishes that are almost impossible to fulfill in their eyes come true. But heavier the wish, heavier the burden.
And the last part is the one Buni likes the most.
And above is a process of fulfilling a wish. Painful even for someone as numb as him —mentally and physically.
Once you take the star in the center, anything that you had in your mind at the moment will come true.
He also has a brother named Hound (a Papyrus Au) thats actively hunting for him....hes also another can of worms I'll talk another day.
(But also, I advise you not to be fooled by the simple waves of colour and the sharpness of swords)
Thats about all :). Thanks for reading if you read all the way here