Peilis

The Doctor adn Skye encountered the Peilis during their adventure in Skye is the Limit

Origin
Peilis are atomic-like creatures that can combine to form almost anything. They feed off of their victims energy, draining them until they die.

Religion
The Peilis worshiped the computer Jezgro, whom they called the core. They believed it to be a living creature. The origin of Jezgro is unknown

History
The Peilis would form links in the mirrors of people of other worlds. They did this for millions of centuries. The Doctor encountered them when they invaded Skye and Bobby's mirrors. The Doctor traveled with the couple into the Peilis world. They encountered Alpha, Beta, and Gamma who where copies of themselves. They met Jezgro, who the Doctor destroyed after Alpha had drained most Skye's energy. The Peilis world was destroyed forcing them to scatter. The Doctor said there wouldn't be enough together to make a pebble.