never received an official release on the Nintendo DS. However, a dedicated community of developers has created unofficial homebrew ports and demakes that allow you to play portions of the game on DS hardware. The State of "Undertale DS"

– Files labeled “Undertale DS ROM” on forums, YouTube, or ROM sites often contain viruses, adware, or crypto miners, especially for such a popular fake title.

You must own the game on PC. Locate the data.win file in your game directory (usually found at C:\Program Files (x86)\Steam\steamapps\common\Undertale\data.win ).