In the MC2 universe in which the daughter of Mary Jane and Peter Parker, May Parker, grew up to become Spider-Girl, it was revealed that when she was still a baby, Harry Osborn had secretly kidnapped her just long enough to clone the child. Not only that, but when he returned one baby (it was never revealed if he kept the clone or the original) he genetically merged the baby he kept with a DNA sample from the Venom symbiote! His plan was to grow the body, then transplant his mind into it to become unstoppable. However, Norman Osborn was killed before that could take place.
Years later the now grown hybrid was found in a stasis pod. After breaking out, she returned to what she believed was her family, only to find May Parker living in her place. There was confusion and tension at first, leading to the new May to fight the “original” May. Things calmed down, and the Parker family accepted the new May into the family. To avoid confusion, she renamed herself April Parker, playing on the joke that both their names are months. But the question remained, who was the clone, and who was the original? Due to her human/symbiote hybrid condition, many believe April Parker to be the clone, but it must be stated, it was never officially revealed which was which, and it seems it can never be truly known.
April Parker had all the exact same powers as May Parker, however she also had all the powers of a symbiote. This included changing any part of her body however she wanted, from changing her face, to changing her clothes instantly into a costume, or even forming her limbs into blades. However she also had the weaknesses of a symbiote, making her extremely vulnerable to sonics and fire.
While at first the relationship between April and May was aggressive, eventually it became sisterly and they teamed up for a while as a red and blue Spider-Girl team. However April eventually started showing more of her symbiote side and took on the name Mayhem after becoming too jealous of May.
In a fight in a warehouse, Mayhem managed to kill Spider-Girl in an explosion, but these actions eventually lead to clones of the Carnage symbiote to take over the world. To prevent all this from happening, April Parker traveled back in time, and transferred her memories of the doomed future to her younger self. This time around when the warehouse fight happened, Mayhem sacrificed herself to save May Parker, and to give her even more peace of mind, Mayhem claimed to be the real clone as she died.
Positively Jim 