Here is a vid showing how to easily get the Marvel Legend Achievement which is for beating arcade without losing a round.
Change the options to the following :
Difficulty : 1 star ( Easy )
Damage : Highest damage
Rounds : 1
Next choose Juggernaut.
Use the following useful moves :
B,DB,D,DF,F 3x Punch ( 41236 LB for XBOX )
Keep using that move over and over. If you have problems you can also hold back and tap Y to get some space.