What is Avatartale?
Avatartale is a community created AU it is also a crossover between Undertale and Avatar. Every character is a bender and Frisk is the Avatar as shown in many images across Google. In this AU Toriel is a firebender alongside Asgore, Sans and Papyrus are both waterbenders along with Undyne. It is unknown what bending Alphys specializes in, it most likely would be metalbending.
Not much is known to me about this AU so feel free to edit and improve - 6DragonSlayer9