Story related, cannot be missed. Remy LeBeau is the boss of the fourth mission of the game, this mission plays in a casino. Tips on defeating Remy LeBeau: Gambit is a tough nut to crack. He shoots from his hands, has a stick with which he can do quite some damage and is pretty fast too. Deadpool might be a bit tougher to beat, but in terms of longevity, Gambit might beat him. You have to a lot of blocking and countering to defeat him. Try to deflect the lasers he shoots from his hands and then lunge towards him. There will be two points where you have to deflect his attacks to advance the fight. The first time he is standing underneath one of the letters of the casino name, the second time he is standing on top of one. There is no use in attacking him at these points, deflect the attacks, so the letters come crashing down and continue the fight.
Note: This fight is sometimes very glitchy. If Gambit disappears, you'll have to restart.