Darkmatter is the boss battle of the fourth mission, Purple Peril.
At the ending of each mission before the fourth mission, Dark Matter is shown to be gathering parts for his plan to grow in power, both literally and figuratively.
He was Amethysto (a hero) who had turned evil somehow. Also you cannot dress up as him from Team supers group store, In the “Purple Peril“ Mission (the 4th mission). Dark Matter can throw cars which can be thrown back by Kinetic, And tanks that can be exploded by Tessla. Also, Captain Roblox can damage him when he smashes one of his arms onto the floating platform. Dark matter is the main antagonist of the game. In every mission, you beat his associates (such as Cicada, Dynamo, and Toxic Waste), but he still gets the parts for the growth machine he needs. If you seen the end before the big bug broke the game, he would revert into a hero and in mission 5, “ Cosminus Chaos “ ( an event mission out of date.) You can become Amethysto.