Mercury is the leader of the Mutacons. Mercury herself is free-spirited, energetic, upbeat, flirty and hyper-outgoing. Mercury thinks that Decepticons in general and Megatron's concept of "peace through tyranny" in particular are roll over the floor, laugh out loud stupid.
Like all Mutacons, Mercury fled the destruction of the Neutronia colony when the Rust Plague hit. In space her starship crew found the Transformation Cog of Amalgamous Prime near a black hole. The mystical object granted them infinite transformation and infinite combination abilities. However they soon found they were beginning to involuntarily merge into one being, slowly losing their own personalities and memories.
Optimus Prime and the Ark crew met Mercury's crew of pirate Mutacons in space.
Mercury communicated with them and offered to trade energon stores in return for help in locating Amalgamous Prime or for the chance to merge with Optimus Prime to learn how to change into his form. (Bulkhead thought that sounded "kinky"). She caused a moderate uproar of whistles and cat-calls among the male Autobots when she visited Prime in person. The Matrix downloaded a history of Cybertron since the Rust Plague to her and she fell on the floor laughing at how dumb the Decepticons were.
Prime promised to help the Mutacons solve their shape-changing problem after the Decepticons were no longer a threat. That was good enough for Mercury and she happily returned to the others and set about delaying the pursuers so the Ark could escape on their way.