This fit so well it's actually worrying.

The original art style of the Darkstalkers games were kind of cartoony in the first place, and If I'm remembering right they used similar color pallets. So that might have something to do with it.

Also tonally speaking whenever Darkstalkers is being more lighthearted it isn't that far off from the tone of your average Danny Phantom episode, and when Danny Phantom is being darker it isn't that far from the tone of the standard Darkstalkers story.

Basically I'm more surprised there isn't more crossover stuff between Darkstalkers and Danny Phantom because tonally and thematically they seem like a natural fit to me.