This is my first time, not sure how to write one out, but basically, this is my one overtly powerful force, and the four beings that could stand a chance against it, and hopefully defeat it.
The Force - Unicron
Unicron can exist across multiple universes, although not simultaneously. Being the size of a planet, he also has the ability to transform into his menacing robot form. Even though in Transformers: The Movie he appears to sustain damage from a variety of attacks, it is stated multiple times that the Matrix of Leadership is the one thing that can truly defeat him.
The Unlikely Super-team:
Godzilla - Even though Godzilla might not be able to survive in the vacuum of outerspace, if Unicron ever found himself stuck on dry land or in water, he might have a problem with this gigantic beast that can not only heal very rapidly for a creature of his size, but also fire his devastating Atomic Breath
Tony Stark - If there ever was a genius with an aptitude for all things robotic, electronic, and digital, the Iron Man is the definitely the one who can analyze a weak spot or invent an effective weapon against Unicron.
Spawn - Wielding the magical and ever-powerful forces of Hell itself, there is no doubt that Spawn would definitely give Unicron a run for his money in the realm of super-powered abilities.
The Joker - For exactly the reasons you'd expect. A random wild-card, with an appetite for chaos that rivals that of the Lord of Chaos. There is no question that the Joker would absolutely interfere with a rival of wanton madness and destruction.