Picking only 4 villains to make a formidable Suicide Squad is tough. I think that for them to be really tough, they have to have powers that work well together. You have to have villains that could destroy on their own as well as on a team, even if it is a messed up, weird, deadly team like the Suicide Squad. So here are my picks and why;
1. Mr. Freeze
Mr. Freeze obviously has the ability to freeze people and things which can be very helpful if you want to make a quick getaway or even if you want to stop someone from making a quick getaway. Freeze has something to live for: his wife. He will complete the mission and could carry the entire team on his back ... or even kill them himself if he finds them to be ... unnecessary. This next villain could do the same if he wanted to.
Doomsday pretty much put Superman in the hospital when they first fought. If he can Superman a run for his money, then you HAVE to have him if you're gonna want any shot at getting a tough task done. Trying to subdue him to get him to be apart of the team would be a problem, but well worth it if you could accomplish it. Not to mention that Freeze could freeze something and then Doomsday could smash right through it, no problem.
Mystique can morph into anyone .... She can literally become the exactly lookalike of anyone!! She can change into a guard or whoever and then take any out with her stealth take downs. She can fight all by herself and she can look like anyone she needs to if she needs to. She can morph into Freeze or Doomsday and make them fight the wrong one and by the time they realize they tried to hit the wrong one - WHAM!! Too late. Night-night, guard!
Megatron is a robot that can turn into a gun. Enough said. Mystique can grab him and shoot at whatever or whoever is in the way and it would be destroyed. Doomsday or Mr. Freeze could grab him and use him, too. Megatron is also awesome by himself. He can fight, transform, and still overcome the obstacle at hand. Mr. Freeze could probably combine some of his technology with Megatron and make an even better weapon. Him and Doomsday could smash through things while Mr. Freeze and Mystique are on their backs. Mystique could even morph into Starscream and use him like in the old show. Think how awesome that would be!!!
So those would be my 4 villain Suicide Squad and why they would be pretty difficult to beat. Just thinking about them all in the same universe is already amazing and it makes me feel like a kid on Saturday mornings when a superhero show would come on. I miss those days. Still, these villains would be an awesome team and make for an interesting comic book, show, or movie, no?