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For two-player video games, if they are physically identical except for color (e.g. the older NES and SNES Super Mario Bros games), you have a Palette Swap on your hands.
Thanks, KD, but I was looking more for the trope The Venture Bos is making fun of - two characters who look similar and act identical, so they have someone to talk aloud to when saying something like "let's investigate the barn".
Edited by Mac_R
I think Identical Stranger also applies here.
Is there a trope for when a work features two main characters whose design and/or personality are very similar?
I've seen it a few times, though it's rarer than it feels to me. In videogames, it's so two people can play and neither be at a disadvantange. In cartoons, it's so the characters can have a friend to use as a sounding board but not introduce more conflict in the plot.