I would like to share with you how i got this achievement in about an hour...First off, to get an arcade mode win, you need to kill only 4 enemies with your character...What made it easy for me is that my character was the only one on the screen...Here is how i did it:
1) the best place to take advantage of my method is early in the game. Play "Wrenchworks" in Act 1. There is a save point before the Omega Base's exterior.
2) As first player ONLY, use the "Change Team" option to remove the other 3 computer characters (leaving only your character)
3)Then resume the game and activate the second controller. As the first controller, go to the start menu -> players -> activate PLAYER 2 (from red button to green)
4) resume the game and you will notice a pop-up window will appear. it informs you that no extra heroes are available for control
5) SAVE THE GAME
6) At "Wrenchworks" there are 10 enemies in the level...defeat the first 4 you encounter to the right of the save point (1 super solider and 2 to 3 AIM troopers)
7) once the 4 or 5 enemies are defeated, head to the exit heading towards the "Omega Exterior" while ignoring the other 5 enemies...That should give you an Arcade win
8) Head back into the "Wrenchworks" and defeat 4 of the 5 enemies left behind (2 super soliders and 3 AIM troopers)
9) Exit to "Omega Exterior" and that wil earn you your second Arcade win
10) Load the last save point and repeat steps 6-10 and the achievement should be yours in an hour or so depending if you skip the score from the Arcade results and how fast you defeat the enemies and run to the exit...
I used the Human Torch and used his "Pick up" special to defeat the first 4 enemies, flew to the exit, returned and beat them again with the "pick up" special and exited...I was able to average 2 arcade wins in about 60-70 seconds...
Hope that helps! Good luck
****EDIT**** as of 24Apr2012...
""I was just using your Marvel: Ultimate Alliance solution for the achievement "The Destroyer". Very good solution, very effective. However, after reaching 100 wins, it did not unlock. I went through the comments and discovered it was because my game froze and, therefore, did not save the previous wins.Please edit your solution and include the warning NoSubs commented so other players who don't read each and every comment before attempting the achievement are aware of the potential dangers of not periodically saving. Thank you.
Comment from NoSubs:
""I agree with this method, but with one adjustment, make sure to save every once in a while (i.e. every 10 wins).
This part of the game seems prone to freezing while loading. The first time I used this method it froze at about 40 wins, I restarted and kept playing and after doing more than 100 total wins (40 before the freeze, 60 after) I did not get credit for the achievement. It seems the wins before it froze were not counted by the game.
However, after loading the last save point in Step 10 of the above solution, once in a while immediately save (i.e. before eliminating any enemies). Then when you are loading the game use that recent save file. It seems that the act of saving a file will save your game's tally of wins. So when my system froze again at about 70 wins I was able to load the most recent save file and only do 30 more to get to 100. So unlike when I was not saving, my wins before the freeze were counted.""