How do you decide who would be a proper character from another developer to cameo in your games? Not asking about how you ask the creators for permission, but what is it that makes you pick that specific character of theirs? What made you pick, for example, CommanderVideo and The Kid for their roles in SMB instead of another dev's characters that could play the same? Wouldn't it be easier to just design your own characters that would play identically to what you had in mind for the cameo chars?

half of the characters in smb i picked because i really loved the characters and designed around them, the rest i kind of needed to fill some design holes and plopped them into place (pink knight/alien hominid/machinarium dude are good examples of that)

designing my own new characters means making up whole little worlds for them and themes or backstories. when i use other peoples characters i get to use an established idea of who they are and kind of mess with it a bit and make them my own.. i really enjoyed that in smb. 

i just really wanted smb to be a celebration of all that got me to where i was and having the cameos we did felt like the perfect way to do it.