What are some interesting ideas for an Undertale and FNAF crossover fanfiction?

One idea could be that the characters from Undertale end up in the FNAF world. For example, Frisk could be trying to find a way to escape the haunted animatronics while also befriending some of them in a similar way they befriend monsters in Undertale. Sans could use his shortcuts to outwit the animatronics' movements. Another idea is to have the FNAF animatronics transported to the Underground. They might be seen as strange new 'monsters' and the Underground residents would have to figure out how to deal with them.

A possible plot could involve the souls in Undertale having some connection to the spirits that are rumored to be in the FNAF animatronics. The main character from Undertale, perhaps Frisk, could enter the FNAF world and try to free the trapped souls. In return, the animatronics could help Frisk in the Undertale world against some powerful foes.

Well, it could be that there is a glitch in the multiverse that causes a fusion of the two worlds. So we have characters like Frisk interacting with Freddy Fazbear. Frisk might try to show the animatronics a different way of living, more like the pacifist way in Undertale. And in the process, they all have to deal with the threats that exist in both worlds, like the purple guy from FNAF and the more malevolent monsters from Undertale.

One idea could be that the animatronics from FNAF end up in the Undertale universe. They might be mistaken for strange monsters at first. The Sans character could be particularly intrigued by their mechanical nature and try to figure out how they work.

An Undertale and My Hero Academia crossover is also a great concept. The heroes and villains in MHA could find themselves in the Underground. Characters like All Might could have interesting interactions with Asgore. And the idea of quirks in MHA and the unique abilities of the Undertale characters could be a really cool aspect to explore, like how Bakugo's explosive quirk might compare to Sans' bone attacks.

One idea could be that the ponies from MLP end up in the Underground world of Undertale. Maybe Twilight Sparkle could use her magic to interact with the magical elements in Undertale, like the SOULs. Another idea is to have Sans and Papyrus meet Fluttershy. Papyrus would be all excited to show off his 'coolness' while Fluttershy might be a bit shy at first but then they could become friends over their love for cooking (Papyrus loves making spaghetti).

The concept of power dynamics is also fascinating. In a 'Undertale Gaster Crossover Fanfiction', Gaster's power, which is not fully understood in the original game, could be compared or combined with the powers of other characters. This might result in epic battles or the need for characters to cooperate in ways they never had to before in their respective stories.

One idea could be that Naruto characters end up in the Underground world of Undertale. For example, Naruto with his determination could be seen as similar to the determination trait in Undertale. He might interact with Sans and Papyrus. Naruto could use his shadow clones to confuse the enemies in the Underground. Another idea is that the ninjutsu in Naruto could be combined with the magic system in Undertale. Maybe Sasuke's Sharingan could have an interesting interaction with the soul mechanics in Undertale.

One idea could be that the characters from Undertale find themselves in the world of Deltarune. For example, Frisk could end up in the Dark World and have to figure out how to get back home while interacting with the Deltarune characters. They might team up with Kris to fight against new threats that are a combination of both universes' villains.

Character interactions are also great. Imagine Frisk from undertale meeting Pikachu. Their personalities are so different. Frisk is this kind and empathetic character, while Pikachu is energetic and curious. Their meeting could lead to all sorts of comical or heart - warming situations. Maybe Frisk tries to communicate with Pikachu in the undertale way, and Pikachu responds in its own pokemon - like way.