When a party member is attacked, Death Rider drains their HP. It is best to use Fire against it. Its attacks are among the strongest of non-bosses and also has fearsome Speed.
Death Rider is usually found on the fifth and sixth floor in Pandaemonium with either a Mythril Golem, which also inflicts massive damage to players and may kill characters who were already attacked by the Death Rider, or in groups of four alongside the Coeurl, which may spell annihilation for the unprepared. Using their weakness to Fire against them works better when focusing on one target at a time. Death Rider can break the damage limit, instakilling a character no matter what. The only other enemies who can do this are the final boss and possibly the Mythril Golem.
Death Riders drop valuable items such as the Thunder Lance and the Ribbon, which makes exploring the Pandemonium easier.