If you are looking for a specific type of gameplay, I can help you find more options. Difficult boss rushes (like Sans or Papyrus fights)? Multiplayer/Online experiences?

But for students at school or employees on a strict network, the biggest hurdle isn't finding these games; it’s accessing them. Firewalls, blocked ports, and "IT-Admin Approved" only lists make playing Undertale: Yellow during a break feel impossible.

Check Scratch: While some animations are simple, many creators have built complex, "extra quality" boss fights on the Scratch engine.

Final Warning: Don't Get Caught

Playing Undertale fan games unblocked is a rite of passage, but keep the volume off (the music is a giveaway) and use a hotkey to hide your tab. The universal "panic key" is Ctrl + W (closes tab) or Ctrl + Shift + T (reopens it later).