If you want more creative control beyond pre-made editors, developers often use more complex engines that can export to Android:

: Allows for complex Lua scripting, enabling high-fidelity recreations of almost any Undertale mechanic. UnderBattles - AU Fights : A collection-style app on Google Play

A fun sandbox for Undertale fans, but manage your expectations

No coding required. Cons: Very limited customization; often buggy; hard to make full games.

where you can design your own boss battles and attack patterns. Key Features

Making quick memes, short animations, or simple boss battles without coding.