The black mechanic wearing a garage mechanics uniform with an R on it that Marlon Wayans would have played was Batman Returns screenwriter Daniel Waters idea to compromise since Tim Burton didn't want Robin involved but Warner Brothers' production chief Mark Canton did so they would have added an aid for Batman but minimized Robin into a mechanic that would have made a cameo in Batman Returns fixing the Batmobile for Batman. Daniel Waters said Tim wasn't enthusiastic about it. Ultimately it was agreed to just leave Robin out again, which is the way Tim Burton wanted it in the first place.
Why was Robin eventually thrown out of your screenplay?
Daniel Waters: "One of our big bonding issues is me and Tim Burton hate Robin. He's just the most worthless character in the world, especially with Tim's conception of Batman as the loner of loners, to have this gushing boy run around, it made us both kind of sick to our stomachs! Mark Canton [Warner Brothers' production chief at the time] was a Robin fanatic and at the first film would sit there mumbling in dailies, 'Where's Robin?'. So we had this black character that works in a garage and helps Batman out of a jam. He's wearing one of those old-fashioned garage mechanic uniforms and it just has an R on it. We really didn't even make reference to it. In fact he helps him out and they have this camaraderie. He drives the Batmobile, which I notice they used in the third film! They didn't even give me a coupon for free popcorn for that!"
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During the Batman commentary Tim Burton said "That was the thing, number one, no Robin. I even think that Bob Kane was happy there was no Robin. It's hard to come up with a psychological profile for a guy wearing a little red outfit with green booties. And all the jokes that come with it. As a kid that's just a part of the mythology is the Batman and Robin jokes. So I thought I'd just avoid all that and keep it pure to Batman's original form."
In the book Burton on Burton Tim Burton said:
In Starlog #145 (1989) Tim Burton about Robin, "We would lift up our arms and say, 'Let's have them both go to Frederic's of Hollywood to pick up that little red and green outfit.'"
Since Tim Burton and Micheal Keaton's version was the first live-action version of Batman since Bill Dozier and Adam West and Burt Ward's campy comedy version, it would have been difficult to include Robin in Burton and Keaton's version of Batman, which was intended to be taken seriously, without getting unintentional snickers, laughs and gay jokes from the audience.