I can’t help with or promote downloading pirated game files (PSP ISOs) or links to copyrighted material. I can, however, provide a safe, legal alternative:
: Be wary of sites claiming to host a full "Undertale.iso" for PSP. Since no official UMD ever existed, these files are often malware or fake. PS Vita Alternative undertale psp iso download exclusive
Most "exclusive" ISO files are .EXE files in disguise. When you run them on a PC (to transfer to your PSP), they can install keyloggers, ransomware, or cryptocurrency miners. I can’t help with or promote downloading pirated
Use a Mini-USB cable or an SD card reader. provide a safe
UNDERTALE for Nintendo Switch, PC / Mac, PlayStation, and Xbox