When have so many stories to pick from, it's hard to nail down just one to put into the film. Luckily for us writers Rhett Reese and Paul Wernick, the same team on the first Deadpool, don't feel like limiting themselves to just one story.
When Cinema Blend spoke to the writing duo about whether or not the sequel would be based on a certain storyline or series, they went into detail on how their process works.
It's how we went about the first one, you know? We dove into all of the runs, and then, you know, fell in love with the character and the tone and the texture. Then we set down the comics and came up with our own storyline, and I think we'll do the same for the second one.
With Deadpool especially, I feel like that particular process is the way to go. Sure he has some great individual stories, and there are some memorable runs as well, but to me, Deadpool is made up mostly of a series of zany and fantastic moments. I don't necessarily reflect on Deadpool like I do, say, the X-Men. I could point you to several storylines right off hand that define them.
For Deadpool I think of moments like the one above, where Deadpool kept a shrunken Rhino on a key-chain, constantly teasing him and putting him in a hamster wheel. Things like Deadpool watching cartoons in the ship when he is supposed to be keeping a lookout (X-Force), or when he carried around his zombified head from the Marvel Zombie-verse.
Cherry picking fun moments and melding them into an overarching story seems like a great fit for this character.