Undertale doctor who Xover. It's gonna be big. Rated T because it might get ugly.

The Doctor finds himself roaming around space and time, like usual, until the TARDIS takes him to the Underground. Once there, the Doctor finds out about the living conditions that all monsters are going through along with what the humans have done for them. When the Doctor first meets the Royal Scientist, all hell breaks loose.

The 12th Doctor had only intended to make sure someone kept their promise. The 10th Doctor was investigating a letter given to him by the mysterious young woman, Snow. The 11th Doctor simply answered a phone call from an old friend. Neither Doctor had any idea what they were walking into until it was already too late. (Formerly WhoTale Cubed)

The legend never reached the Daleks' communications.

In an AU where the eighth human never fell into the underground, The Tenth Doctor saves the underground from the clutches of Asriel Dreemurr. But a new threat from outside the Underverse is threatening to take over. With the Undertale universe being threatened by its parallels and the outcomes they bring, the Doctor needs a companion. The Royal Guard was nothing compared to this.

Papyrus cooks, Sans is scienc-y, and the human is missing. Irving continues to investigate.

The Doctor expected trouble when he went to investigate time anomalies disrupting the underground. What he didn't expect was a blue eyed skeleton with the intent to kill. Slight pacifist and genocide spoilers. More like K-plus, but T to be safe.