Where Can I Find New Undertale Stories With Crossover Themes?

Honestly, AO3 is basically the holy grail for that kind of thing. Their tagging system is a lifesaver—you can just search "Undertale" and filter by "Crossover" or add another fandom tag like "My Hero Academia" or whatever you're into. The volume of stories there dwarfs everything else. I've found some truly bizarre but delightful crossovers, like a 'Deltarune' meets 'The Magnus Archives' fusion that had no right being as creepy-good as it was. That said, don't sleep on FanFiction.net either. Their crossover category is a bit more old-school and less precisely tagged, but scrolling through the Undertale section there still yields some classics from when the game first blew up. The interface feels dated, but some writers never migrated. I stumbled upon a surprisingly heartfelt 'Undertale'/'To the Moon' mashup there last year that I haven't seen reposted anywhere else. Tumblr can be a weird little side avenue, but it's hit or miss. A lot of writers will post snippets or links to their AO3 works, and sometimes you find threads or asks about crossover AU concepts that never got fully written but are fun to think about. It's more for the vibe and inspiration than a proper library, though.

Ohhh, Undertale crossovers are my jam! I love how creative the fandom gets with blending its characters into other universes. My go-to spots are Archive of Our Own (AO3) and FanFiction.net—they have filters for crossover tags, so you can hunt down 'Undertale' mashed up with anything from 'My Hero Academia' to 'Harry Potter.' Tumblr’s also a goldmine if you dig deep; some writers post snippets or links there. For niche stuff, I’ve stumbled on gems in Discord servers dedicated to Undertale RP or indie game crossovers. Wattpad’s hit-or-miss, but sorting by kudos or comments helps. Pro tip: try searching 'UT/XYZ' (replace XYZ with the fandom) on Google—sometimes smaller forums or personal blogs pop up with hidden treasures. Honestly, half the fun is the hunt!

I don't know if I'd call them 'top' because that feels a bit official, but the ones I keep going back to all have a shared foundation in the core AU concepts like 'Glitchtale' or 'Underfell' crossing over with something else entirely. There's this older one, a behemoth of a fic, where the 'Dusttale' version of Sans ends up in the 'My Hero Academia' universe. It's less about power-level comparisons and more a bleak character study on guilt and finding a purpose after you've... done the unthinkable in your own world. The writer nailed Sans's voice, all weary sarcasm masking a bottomless self-loathing, and watching him interact with a world built on heroic ideals created this fascinating friction. Another crossover that doesn't get enough love is with 'The Magnus Archives'. Think about it: a universe where fear literally creates monsters, meeting a universe where monsters are born from concentrated emotion and intent? They blend almost too well. I read one where Frisk, post-pacifist, becomes an avatar for The Eye, and the way their SAVE/LOAD ability was re-contextualized as a terrifying paranormal power gave me chills. It leans hard into cosmic horror while keeping the soul of the characters intact, which is a tough balance.