The Experiments are three characters similar to the Titans. The Experiments all carry big, bulky weapons and often have tons of machinery behind their backs. The first, Uirusu, appeared in the Mysterious Five Project as a boss and unlockable character. Called the queen of viruses, she carries a mobile lab on her back to create viruses and inject them into opponents.
The other two, named Strass and Vodorod, appeared in Grand Theft Gumball as bosses and unlockable characters. Strass sleeps until she wakes up, killing everything in sight by running into it with her blades. She also carries four turrets on her back, making her effectively a tank. Despite carrying such heavy weapons and equipment on her back, she is still quite speedy.
Vodorod appears in Grand Theft Gumball as well. She is based off the element of hydrogen, using metal weapons such as a buzz-saw and a sword. Her weapons appear to be melting, creating molten hydrogen bubbles and puddles wherever she goes, and she can suck in these bubbles and puddles at any time. Out of the three, she is probably the most balanced in all directions.
The experiments all carry heavy machines on their backs. It is unknown beyond attacking what purpose they serve, but a good guess would be that it is their life support. They are unknown in origin, and they all appear to be female.