Marvel Ultimate Alliance 2

There are a total of 276 fusions in the game. The best way to get through this quickly is to unlock every character first and use Sim Mission 1 to quickly knock them all out. At the end of the mission, you can choose when to use the exit console and you have unlimited fusions as well as swap characters, so you can do them all right in a row. I found using this list helpful. Start with Captain America and do a fusion with every character running down the left side. Then switch your main character to Daredevil and continue down the list. You won't use Cap again obviously as you paired him with Daredevil when he was your main. Then do Deadpool the same way, skipping Daredevil and Cap who are above him. And so on down the list until the achievement unlocks. Each character will go more quickly as there are fewer people they need to pair with.

NOTE: This does not count the "DLC" characters: Black Panther, Cable, Carnage, Juggernaut, Magneto, and Psylocke. Skip them when combining fusions.