Complex sentence: During this time, Cemetery Wind, aided by Lockdown, a Cybertronian bounty hunter who is hunting down Optimus Prime for unknown reasons, tracks down and mortally wounds Ratchet, who is then killed by Lockdown after refusing to expose Optimus' whereabouts.
Split into simpler sentences: During this time, Cemetery Wind are aided by Lockdown, a Cybertronian bounty hunter, who is hunting down Optimus Prime for unknown reasons. Together, on one occasion, they track down and mortally wound Ratchet, who is then killed by Lockdown after refusing to expose Optimus' whereabouts.