Taylor Hebert might be a strong candidate. Her ability to control bugs gives her a wide - ranging and somewhat unpredictable power. She could potentially use her bugs to disrupt Pennywise's illusions or to find him when he's hiding. Also, her experience with facing difficult situations in the 'Worm' world could give her an edge in dealing with Pennywise.
I think Alexandria could be a good contender. She has super strength, speed, and durability. If she could somehow resist Pennywise's fear - based attacks, she could physically overpower him. Her no - nonsense attitude from the 'Worm' universe might also make her less susceptible to Pennywise's mind games compared to other characters.
Talion would be a very interesting character to crossover. His skills as a ranger and his connection with the wraith are quite unique. In the Worm universe, he could use his combat abilities and stealth to great effect. He might be seen as a wildcard by the different factions in Worm. His sense of justice, developed in Shadow of War, could also put him at odds with some of the more villainous characters in Worm.
Zero and Ruby would be a likely pairing. Zero is a powerful and skilled fighter, and Ruby has a lot of potential and a unique weapon. They could learn from each other's combat styles. Ruby could learn about Zero's more serious and battle - hardened approach, while Zero could be inspired by Ruby's enthusiasm and creativity in fighting.
Ryuga could also be a main character. His dark and mysterious nature would add an interesting dynamic to the crossover. He might initially be at odds with the beywheelz characters, but as the story progresses, he could see the value in working together. Plus, his powerful beyblade skills would be a force to be reckoned with in the new and different battles of the beywheelz world.
I think Ruby and a young, adventurous Pilot would make a great pairing. Ruby's enthusiasm and eagerness to learn new things would mesh well with a Pilot's daredevil nature. They could exchange stories about their respective worlds while fighting side by side.
One idea could be that the characters from 'Worm' encounter Pennywise in their city. Maybe Taylor Hebert, with her power, tries to figure out a way to combat Pennywise's illusions. Another idea is that Pennywise targets the parahumans in the 'Worm' universe because they have unique fears due to their powers.
Ruby could also be a great candidate. Her natural leadership skills and her ability to quickly adapt to new situations would serve her well. Plus, her speed and agility could make her an excellent Pilot. She might even come up with new strategies for using the Titans in combat, inspired by her own experiences in RWBY.
Natsu would be a likely candidate. He's always up for a challenge and not afraid to take on powerful opponents. He'd probably be the first to rush towards Godzilla, either to fight it or try to befriend it in his own Natsu - like way.
Luffy. He's always open - minded and eager to make new friends and allies. When he sees a Sekirei, he won't be judgmental about their strange appearance or powers. Instead, he'll be excited to have them on his side and will immediately start planning some grand adventure or battle together.
I think Lynn could also survive. She's tough and athletic. If it came down to it, she could probably outrun the animatronics or even fight them off physically. She's not one to back down from a challenge, and in a FNAF - like scenario, her physical abilities would be very useful. However, she might need to learn to be more strategic as the animatronics are not your typical opponents.
Tattletale from 'Worm' could be an extremely interesting addition. Her power of hyper - awareness and her devious nature could make for some really intense interactions with the characters in 'Persona 4'. She could either be a great help in solving the Midnight Channel mystery or a major obstacle, depending on her motives.