Undertale Yellow is a free fan prequel to Toby Fox's indie hit seven years in the making, and it's just released to massive fan acclaim.

A new Undertale fan game, called Undertale Blue, has been announced by a team of indie devs following the success of the Yellow fan game.

Toby Fox's Undertale is intentionally vague with much of its narrative, which has allowed fans to come up with these fascinating theories.

Undertale, the quirky, pixelated adventure game, became a smash hit when it came out because of its unique mechanism: You can talk to its monsters and show them mercy, rather than killing them.