just means you have to do a fusion once for every character, with every other character in the game. so Cap has to do one with Daredevil, Deadpool, Gambit, etc on down the line with everyone, Daredevil has to with Cap, Deadpool, etc. there are over 250 something combos. it shows in the stats for each character how many unique fusions they have done so far. also one of these threads has a really nice spreadsheet you can use to check off when 2 characters do a fusion.
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