(Sorry for bad english, :p)
(Please don't say that MV or VX have already an Undertale system, I know, thanks.)
Engine: RPG Maker XP
A fan-sequel/game of Deltarune, a game by Toby Fox.
DELTATALE is a game with an engine made from zero using RPG Maker XP and Ruby systems.
Early try to draw our Demon Countess, who destroyed her own soul leaving just an empty shell of a body - until our heroine unwillingly takes possession of it, every time she falls asleep.
(I know it’s a premade face from the Dark Fantasy Set, but I spent so much time with her, that I can’t bring myself to change the sprite anymore xD)