Unit 686 was a Space Pirate mentioned in Metroid Prime 2: Echoes. An injury report in the Space Pirate mining facility stated that he had released a Tallon Metroid for use as target practice, and was assaulted by this Metroid. Somehow, he survived the attack, but was left with brain damage that would heal in a cycle. What became of 686 is unknown.
"Injury Report 07.200.07
Unit 686 released a Metroid for target practice today: the Metroid then assaulted 686. He should be regaining brain functions in a cycle."