Undertale 2-players battle BETA by Liaaah - Game Jolt

Undertale Bits and Pieces Together (2-4P) [UNDERTALE] [Works In Progress]

Undertale Fight Simulator (Create Your Battle !) by NutelGame - Game Jolt

Baldi Battle in Undertale Fan Game by sxdg - Game Jolt

Game Jolt - Share your creations

Undertale: Glitchtale Fighters (2 PLAYER) by A_Okay_Dev - Game Jolt

I made an Undertale fighting game! It's called Brawltale and it took a lot of work over a long period of time, here's some screenshots from the game and if you're interested

Game Jolt - Share your creations

undertale multiplayer by bili_chara - Game Jolt

Game Jolt - Share your creations

Undertale Together: 2 Players by Aes_Ren - Game Jolt

Best Fan Games - Game Jolt

Image 8 - Undertale Together (Two players Mod) for Undertale - ModDB

Best Fan Games - Game Jolt

Best Fan Games - Game Jolt

Game Jolt - Share your creations