Ahsoka Tano would be an excellent addition. She has a rich history in the Star Wars universe, from the Clone Wars to her later appearances. Her wisdom and combat skills could be a great asset to the Rebels in a crossover. She could also provide a link between different eras of the Star Wars story.
Boba Fett would be a cool character to throw into a Star Wars Rebels crossover fanfic. His bounty hunter skills and his own vendettas could create some interesting plotlines. Maybe he's hired by the Empire to take out the Rebels, but then has a change of heart and ends up helping them instead.
Definitely Darth Vader. His presence would create a lot of tension. He could be on a mission to hunt down the Rebels crew, and it would be a battle of wits and strength as they try to outmaneuver him.
Naruto and Ezra would likely be main characters. They are both young heroes on a journey of self - discovery.
Definitely the Lotus from Warframe. She could be like a wise advisor to the Jedi Council, sharing her knowledge of the Orokin and the Tenno. And Darth Vader would be a great addition too. Imagine the confrontation between him and a powerful Warframe like Excalibur. It would be an epic battle of light and dark powers.
Definitely include Obi - Wan Kenobi. He has a connection to Geonosis already from the movies. Anakin Skywalker would also be a great addition. And for a non - Jedi character, you could add a Geonosian rebel who is trying to overthrow the corrupt leaders on the planet.
Well, Sabine Wren from Star Wars Rebels would be a great candidate. She has a strong connection to Mandalorian culture already. She could interact with Din Djarin from The Mandalorian. They could exchange stories about their experiences with Mandalorian traditions and perhaps even team up to fight against the Empire.
You could include characters from other crime - themed games like Tommy Vercetti from Grand Theft Auto: Vice City. His experience in the crime world could create some interesting dynamics with the Mafia 3 characters. They could either be rivals or form an uneasy alliance.
Definitely Luke Skywalker. He could bring his Jedi wisdom to Earth and teach people about the Force. Han Solo would also be great. His roguish charm would be fun to see on Earth. And of course, Darth Vader. His imposing presence would create a lot of drama.
Han Solo and a Skaven from Warhammer. Han's roguish charm and ability to get out of tough situations could be pitted against the devious and sneaky Skaven. The Skaven's underhanded tactics and Han's quick thinking would make for some really entertaining encounters as Han tries to outwit the Skaven in various situations across the two universes.
One idea could be a crossover with the original Star Wars trilogy characters. Maybe the Rebels crew teams up with Luke Skywalker and Han Solo to take on a new, powerful Sith threat. This would bring together the scrappy underdog feel of the Rebels with the classic heroism of the original trilogy.
I think pairing Kanan Jarrus and Dumbledore would be really interesting. Dumbledore is this wise and powerful wizard, and Kanan is a Jedi with his own set of skills and knowledge. They could have deep discussions about leadership, the nature of good and evil, and how to train the younger generation. Kanan could learn from Dumbledore's teaching methods when it comes to mentoring Ezra, and Dumbledore could gain insights into the Force from Kanan.