The main protagonist of my comic is starting to work for an evil company in the next strips. At the same time, he has joined a secret do-gooders' organization, whose leader is a weird monk, so it's a good time to offer cameos as clients, co-workers or members of the organization.
In short, you get to choose between "good" and "evil", in a sort of ying and yang.
The requirements: Human appearance.
Of course, authors will be cited, links provided,.. You know the drill.