Scaramouche the Merciless is an android who used to be Aku's #1 assassin. He is now Aku's #3 assassin since Deathblow and Da-Bomb took his top place. He is also an antagonist from season 5 of Samurai Jack on Adult Swim.
By the time Jack reaches the plume of smoke, he arrives at a ruined city, filled with rubble and the corpses of its dead citizens. Jack meets the robot assassin named Scaramouche, who claims himself to be Aku's most favored assassin and remarks on Jack's nigh-unrecognizable appearance, including the loss of Jack's sword. In a flashback, Jack recalls his signature weapon falling down a pit as he looks in horror. Laughing, Scaramouche declares that Jack is no threat without his sword, and calls Aku on his mobile phone to make a report, but Jack destroys the phone with a thrown kunai.
Satisfied with this turn of events, Scaramouche begins to fight Jack, first by playing a magical flute that forms a golem out of the city's rubble. Jack quickly discovers that Scaramouch can rebuild the golem easily by reanimating more rocks to replace any part he breaks off. Landing among a pile of rocks after destroying the golem, Jack is once again swept up in another hallucination, this time seeing the rocks around him as the children of the city, begging him for help. The mysterious rider (prevalent in his other visions) universally looks down on the scene. Jack pleads for their understanding, which made Scaramouch thinks Jack has gone "beaucoup cuckoo". Eventually, Jack destroys the flute, but Scaramouche reveals that his voice was the true source of his magic. The robot proves his point by scatting. This impromptu singing animates Scaramouche's sword to continue the fight against Jack.
While Jack barely dodges the sword's attacks, Scaramouche brings out another blade which opens up like a tuning fork, demonstrating its ability to vibrate at a frequency powerful enough to shatter Jack's own knives. As Scaramouche fights Jack to a standstill, he gloats over his victory, but Jack throws his remaining sword at Scaramouche, still vibrating from clashing with the tuning fork sword. The sword explodes at the last second, severely damaging Scaramouche's vocal chord equivalent, leaving him unable to fight. Scaramouche admits defeat as Jack cleaves him in two with Scaramouche's first blade, after which Jack keeps the tuning fork sword for himself as he leaves.
It's revealed that Scaramouche survived as a head all along. Upon awakening in the ruined city, he cheers up himself about being alive but finds out his phone is broken and he is unable to contact Aku to tell him about Jack having lost his sword. As Ashi is traveling to find Jack meeting with people he helped back in the past on her way, Scaramouche travels as a bouncing head trying to find a way to communicate with Aku and finds a boat which he decides to use to reach Aku, but is delayed by a sailor because the rules were only those who have a body can board the boat. It also turns out that Scaramouche is only #3 on Aku's Current Top Assassins list (he's behind Deathblow and Da-Bomb). Scaramouche manages to get on the boat after many failed tries by having another guy with a head small enough to fit Scaramouche to be "his body".
Scaramouche then finds a telephone booth (somehow in the future) and goes to call Aku. Aku does answer, and as Scaramouche tells him that Jack's lost his sword, Aku can't hear it because of all the chatter going on the boat carrying crowds. Frustrated, Scaramouche lashes out at the dog passengers talking to shut up already, and before he can finally tell Aku, one of the dogs grabbed Scaramouche (Aku hangs up the call afterwards) and threw him off the boat into the water.
Time later, Scaramouche took control of a squid and arrived at Aku's lair, where he informs the Master of Darkness about Jack losing his sword. As a reward, Aku restores his body and both dance together. Unaware that Jack had recovered his sword, Aku and Scaramouche confront Jack and Ashi, but after seeing Jack with his sword, Scaramouche tries to explain he didn't have it when he last saw him before Aku angrily explodes his head with his eye beam, killing him.