One idea could be that the characters from Homestuck end up in the Underground of Undertale. They might have to deal with the various monsters there while also trying to find a way back home. Maybe John Egbert could team up with Frisk and they use their unique abilities to overcome challenges like puzzles and battles.
Frisk and Dave Strider would be an interesting pairing. Frisk is all about kindness and determination in Undertale, while Dave is this cool, sarcastic guy from Homestuck. Their different personalities could lead to some really fun interactions, like Dave trying to be all cool while Frisk just goes about their business of being kind to everyone.
A good plot could involve a villain from the Homestuck universe creating chaos in the Avengers' world. The Homestuck characters come to help, but there are misunderstandings at first between them and the Avengers. However, as they start to understand each other's powers and motives, they form a strong alliance to defeat the villain.
One common theme is the exploration of different cultures. In both Steven Universe and Homestuck, there are unique cultures. In crossovers, it's interesting to see how the Crystal Gems' way of life and values interact with the trolls' or the kids' in Homestuck. For example, the idea of friendship and loyalty is strong in Steven Universe, and it can be contrasted or combined with the relationships in Homestuck.
To write this kind of fanfic, start with a strong hook. Maybe start with Steven waking up in the Underground or Frisk arriving on Earth near Beach City. Then, build the story gradually. Show how the characters react to the new environment and each other. Don't forget to add some action and conflict. It could be a battle between the Gems and some of the more aggressive monsters from Undertale. And make sure to stay true to the essence of both universes. Don't change the core personalities of the characters too much. This way, fans of both shows will be able to enjoy your fanfic.
The cultural clash. BNHA has a modern, superhero - like society with hero agencies and rankings, while Undertale has a more fantasy - based, underground world with its own set of rules and moralities. In a crossover fanfic, seeing how the characters from each world adapt to the other's culture is really interesting. It can lead to some really fun and thought - provoking situations, like how the BNHA heroes would deal with the monster - human relationships in Undertale.
I really liked 'BNHA: Undertale Edition'. In this fanfic, the author does an amazing job of transplanting the BNHA characters into the Undertale universe. They face off against the classic Undertale foes but with their own BNHA - style abilities. It's full of action - packed battles and some really heartwarming character interactions.
John Egbert and Spider - Man could be an interesting pairing. John's ability to manipulate wind and his generally positive attitude could contrast well with Spider - Man's quippy and more street - level heroics.
A possible Undertale and Steven Universe crossover fanfic could be really interesting. It might involve characters from both universes meeting in a strange new world. For example, Steven could end up in the Underground from Undertale. He would probably try to use his powers of peace and love to resolve conflicts there, like how he does in his own show. Maybe he'd meet Sans and Papyrus, and there could be some really funny interactions. Sans with his laid - back attitude and Steven's positive energy would make for a great comical duo.
One creative storyline could be where the characters from Batim end up in the Underground of Undertale. Maybe Bendy and his crew are mistaken for strange monsters by the Undertale characters at first. They then have to navigate through the various areas of the Underground, facing challenges like the puzzles in the ruins or the battles in Snowdin, all while trying to find a way back to their own world. Another idea is that the Ink Machine from Batim somehow gets connected to the Determination power in Undertale, causing all sorts of wacky and unexpected interactions between the two universes.