While Mark Lilly has been cloned more than once, Clone Mark successfully trades places with him for several days by knocking him out and putting him in the closet, in the episode "Attack of Mark's Clone".
He is something of a sadist as he likes to slap people with a glove. He engages in Callie's particular form of torture sex much more readily than the real Mark. Callie remarks that he is a "surprisingly forceful dominatrix".
Despite these differences, Clone Mark still has a lot of Mark in him, sharing his love eggs and Ferris wheels. He also refrains from cursing which caused Callie to remark that mark's swearing rule was "literally in his DNA".
He was apparently created by Callie Maggotbone to help her team win a bowling tournament since Mark is a notoriously bad bowler. Clone Mark dyed his hair blonde at Callie's suggestion. Clone Mark soon heads to the original mark's apartment where he knocks him out and places him in the closet on Callie's orders. He then proceeds to the real mark's place by scaring and bullying Randal for using his possessions as well as his attempts to bully him.
When Clone Mark finds out that Callie will "make sure Clone Mark is sleeping with the fishes in the Hudson!" once she wins the bowling tournament, he kills Twayne Boneraper's assistant Tad Monkeybottom with Callie's trident and frames her for the murder.
Francis Grimes eventually discovers the real Mark in the closet, but is crippled and blinded while dealing with the clone. Clone Mark gets away.
Clone Mark met a call girl and was disappointed she was blonde as he requested a red head. As the call girl got sad, he told her they'll make it work. But Mark Lilly manages to lead Grimes to catch the clone near a ferris wheel. The two marks fight before Grimes shoots both of them in the arm and takes the clone to jail.
Clone Mark is put to death for murdering Tad. Before his death Callie talks to him and claims that her comment about "sleeping with the fishes in Hudson" was really giving him a free cruise ticket around the world. He is executed and his body parts are harvested to help Grimes (who was blinded and his legs crippled) and Leonard Powers (who got his chin pierced by a minotaur). Twayne enjoys eating Clone Mark's tongue saying, "That has some kick!" Randall Skeffington requests the rest of the clone's remains be put in a doggie bag.
- Mark Lilly was previously cloned twice in the episode "Hell for the Holidays". The first one was made by Callie with Brooke's help so as to replace the real Mark to fight in the blood court, but was discovered by Mark and swiftly destroyed by Aldermach Maggotbone. Mark subsequently made another clone and sent him to the fight against Twayne Boneraper in his place. The second clone got killed quickly.
- Grimes had the thought the difference between the two Marks were the different color eyes until the original pointed out it was his hair. At the end, Grimes realized his mistake of not putting the hair into factor.
- Mark was put off by his clone's death, as it was like watching himself die and became disturbed by the eerie sight.