Definitely Twilight Sparkle could be a main character. She is intelligent and her magic skills would be useful when dealing with the unknown world of robots. Also, a friendly robot like B - 12 (from a different robot - related story) could be a main character. They could form an unlikely duo to explore their combined world.
Another possibility for main characters could be Rainbow Dash from MLP and Blastoise from Pokemon. Rainbow Dash is brave and loves adventures, which would be perfect for exploring the new Pokemon world. Blastoise is strong and reliable. They could form a great team, with Rainbow Dash using her speed to scout ahead and Blastoise using its water attacks to protect them from danger.
Well, in this fanfic, the ponies might be on a quest to find a special crystal that is lost in the robot - dominated land. The robots, on the other hand, think the ponies are invaders at first. But as they interact more, they realize the ponies' good intentions. The ponies help the robots understand the concept of friendship and in return, the robots use their advanced technology to help the ponies locate the crystal.
Twilight Sparkle and Luke Skywalker could be main characters. Twilight's knowledge of magic and her inquisitive nature would make her a great counterpart to Luke's Jedi training and his journey of self - discovery. They could learn from each other and face challenges together.
Peter Parker (Spider - Man) and Rainbow Dash could also be the main characters. Rainbow Dash's boldness and flying skills combined with Spider - Man's powers would make for an exciting duo. They could compete in friendly challenges while also saving the day in both their worlds.
Pinkie Pie would be an obvious choice as she is closely associated with cupcakes in the MLP world. She could be the lead character, coming up with new cupcake ideas and spreading her love for cupcakes throughout Ponyville.
Fluttershy and Big Macintosh would be an unexpected but sweet choice for main characters in an MLP wedding fanfic. Fluttershy's gentle nature combined with Big Mac's quiet strength would create a really heartwarming story. And all the farm animals that Fluttershy loves and Big Mac's family on the farm could be part of the wedding, adding a unique touch to the story.
Obviously, Starlight Glimmer would be the main character as it's her revenge. But Twilight Sparkle could also be a major character. Since Twilight is often the mediator in Ponyville, she would be the one trying to stop Starlight's revenge and make her see reason.
Ganondorf from Hyrule Warriors could be a very interesting main character in this fanfic. His villainous nature could create a lot of conflict in the MLP world. On the pony side, Fluttershy could be a main character. The contrast between her gentle nature and Ganondorf's evil would be quite fascinating. And perhaps a character like Midna from Hyrule Warriors could also play a major role, using her unique abilities in the MLP world.
Pinkie Pie would be a great main character for a disco light mlp fanfic. She loves parties and having fun, so when she sees the disco light, she would go wild. She could be the one to organize all the disco parties around the disco light and get all the other ponies involved.
Twilight Sparkle could be a main character. Since she is very intelligent and curious, she might be the one who gets drawn into the Creepypasta - related events. Her knowledge of magic could also play a crucial role in either solving the problems caused by the crossover or in getting trapped in the first place.