Undertale - Homosuck is not Undyne’s favorite anime. One of the characters is a lamer 2edgy4u version of her.

Toby Fox is not just a fan of Homestuck, he's the guy who makes the majority of the music for it in things like the flash animations/games, and the companion soundtracks that offer theme music for the characters or certain situations in the comic.

Guy has been friends with Andrew Hussie for years, and Hussie's even joked that Toby began development on Undertale while living in Hussie's basement.

AG: I just want my goddamn theme song back from that douche8ag skeleton!