The most popular method is using Android ports of "Create Your Frisk" (CYF), a fan-made engine for creating custom battles. How it works: These are often
Feasibility and Overview of “Undertale Battle Maker” for Android undertale battle maker android
menus, along with advanced scripting options for attack behaviors. Community Hub : You can download and play over 800 user-made bosses through the Battletale Custom Bosses UNDERTALE Create! The most popular method is using Android ports