Even More Challenges
Challenge #1: Miss Kobayashi's Dragon Maid/Hortensia Saga: Theresia is sent to the Dragon Maid world and is taken under the wing of Tohru, Lucoa, and the others. Just throwing this out there because Theresia turns into a gigantic dragon and is really hot, especially when she turns from dragon to human and is completely naked. I'm sad that Hortensia Saga has no TV Tropes page or any fics on this site or Archive of Our Own.
Challenge #2: Miss Kobayashi's Dragon Maid/Fate Series: Any of the Servants who turn into dragons like Sieg, Tiamat, Virtra, and/or Oryou land in the Dragon Maid world. Inspired by the story Miss Kobayashi Magus Neighbor by Mundatorem.
Challenge #3: Date A Live/Seven Mortal Sins/Seven Heavenly Virtues: Shido and the Spirits meet Maria Totsuka and get caught up in the conflict between the Devils and Angels.
Challenge #4: Isekai Sniper is the Female Warrior's Mofumofu Pet/Final Fantasy VII Remake: The Isekai Sniper characters find themselves in Midgar or the Final Fantasy characters find themselves in the Isekai Sniper world. Throwing this out there because the Isekai Sniper character Erika Hardlock looks exactly like Tifa Lockhart and is basically an expy of her (super strong martial artist, her first shown mission is infiltrating a perverted crime boss' hideout by pretending to be a slave girl, said crime boss is called Don Cordero which is similar to Don Corneo). Aerith, Tifa, Jessie, and Yuffie would likely think Mofuo is cute because he looks like a teddy bear and Mofuo would likely bond with Barret because of their mutual love for guns.
Challenge #5: Superman/Lone Wolf: Kal-El's rocket lands on Magnamund and he is raised and trained by the Kai Lords. He could either replace Lone Wolf or be another survivor of the Kai massacre. Feel free to pick his name. I'm pretty sure Magnamund has a yellow sun, so he'd have his powers, but the story would still be balanced because every major threat is magical or demonic, so his invulnerability would be useless and he would have to be careful in battle. Him with the Sommerswerd, the Sword of the Sun, would be awesome.