As you know there is a Moviepilot contest going around regarding what group could defeat who in a showdown. Being a huge Transformers fan, I like to wonder which member of different continuities could defeat the Transformers. I'd say the biggest bad of them all and the most unique Transformers villain is Unicron. Despite his stature and strength, he is only well known by huge Transformers fanboys, making him kind of underrated. If you are one of those people who don't know who he is, here is IGN's description of Unicron on their "Top 25 Transformers" list.
Unicron is Galactus and the Death Star rolled into one. He’s far more massive than your typical Autobot or Decepticon, and he can transform into mechanical planet as he goes about his job of devouring reality. Plus, he was voiced by Orson Welles (in one of his final acting roles). That certainly helped Unicron leave an impression when he debuted in Transformers: The Movie.
Since that debut, Unicron’s backstory has been fleshed out a great deal more. We now know that he is no less than the god of chaos, locked in an eternal struggle with his twin, the god of order named Primus.
Anyway, now that I just explained to you the nature of Unicron, here is my list of beings who definitely could bring Unicron down.
To start my list off, I am going to discuss a very HULKING possibility (ha, ha, is this funny? I'm very sorry for my poor attempt at humor). The Hulk is obviously a powerhouse in the Marvel universe, which is why he could take on the giant of the Transformers universe. Let's face the Hulk is so strong he can do many things. He survived a nuclear bomb, held up a 150 billion ton mountain, and for the win, destroyed an asteroid two times the size of Earth as seen below. That being said, he can clearly destroy Unicron easily.
Clearly this is a very extreme example of who can beat who. God has been portrayed and voiced many times in film, television, audiobooks, and radio. Plus, there has been a series of Bible translations, qualifying God to be used. According to the Bible, God is wise and mighty as said in Job 9:4 "He is wise in heart and mighty in strength - who has hardened himself against him and succeeded?" So, this may be a cheap shot but dammit it works. God can and will instantly destroy Unicron. Hallelujah!
Magneto would definitely tear Unicron to shreds. As you know, Transformers are metal, plus Cybertron and Unicron are both 100% metal. The way I see it, you would need to transport Magneto to space. Then, we let the battle happen. In just five seconds, Magneto could just grip his fist and turn Unicron into a ball of metal. Better yet, Magneto could force Unicron to remain in his Cybertronian moon form permanently. Pretty much it would be a fight Magneto would instantly win.
Obviously, compared to Unicron Batman just seems like a man. Although, this is the same man who once defeated the Hulk (outside continuity) and the Hulk is more than enough qualified to defeat Unicron. While we don't know how Batman could defeat Unicron (he could use gamma radiation, seek the power of God, become a mutant, etc.) we do know that he is the man with a plan. He could use his detective skills to defeat Unicron and figure out some sort of weak point. With his strength and intellect, he would definitely have the upper had. Cause, you know, he's Batman!