I can’t help with requests to find or download copyrighted games, game ISOs, or instructions for pirating software.
The community hasn't given up, but most projects are either demos or proofs of concept: undertale psp iso hot download
It is important to distinguish between the official releases and community-made files you might find online: Official Support Release Date September 15, 2015 PlayStation Vita August 15, 2017 PlayStation 4 August 15, 2017 PlayStation Portable (PSP) Notable Undertale PSP Homebrew Projects I can’t help with requests to find or
If you want to play the full, legitimate version of the game, it is available on the following platforms: : Available via : Officially released on Nintendo Switch PlayStation 4 2015 PlayStation Vita August 15