"Night of the Raving Dead"
Sam and Max are sent to investigate Jurgen's club The Zombie Factory in his castle in Stuttgart. He organizes an elaborate death trap that would imprison live partygoers and extract their souls for an exchange with Hell. What he gets in return is never said exactly but the occurrence does leave him with the bodies of the victims with which he intends to create a massive zombie army. In the meantime though, Jurgen focuses on constructing his Frankenstein's Monster-esque creation and appearing as hip as he can be. Sam and Max naturally exploit this to weaken Jurgen, such as endorsing Garlic Clove Cigarettes on their show Midtown Cowboys, which Jurgen is an avid follower of, despite what garlic does to vampires.
He entraps Sam and Max in the soul-extracting process, causing them to become zombies until the two can retrieve their souls. They force him through the same process, his own soul being extracted and his plot foiled.
Other Appearances in Season 2
In "Chariot of the Dogs", Jurgen appears on the ship of T.H.E.M. (an organization of three mariachis who transfer the souls to Hell in exchange for powering their spaceship). Jurgen's soul is put through the process and sent to Hell. In "What's Up, Beelzebub?", Jurgen appears in Hell as the receptionist. He sarcastically notes that he'll get Satan to meet with Sam and Max in order to spite them for foiling his plan. Presumably, he remains in Hell from that point on, save for the cameos later.
He appears in the crowd scene at Sybil Pandemik and Abraham Lincoln's wedding, trying to catch the bouquet but being beaten by Max to the punch.
"The Tomb of Sammun-MakJurgen prior to his vampiric state appears as an antagonist in the second episode/game of Season Three The Devil's Playhouse. In 1901, he appears trapped in a bas relief within the tomb of Sammun-Mak by a moleman curse. He appeals to Sam and Max's ancestors Sameth and Maximus to help him escape his imprisonment and leaves them entrapped when the bas relief curse takes them.
Jurgen reappears on the Disorient Express heading back home and is suspected of having stolen the Devil's Toybox from the two. He fills his cabin with many anti-vampire charms and garlic in order to ward off a vampire curse another moleman placed upon him. Wanting to search his cabin for the Toybox, Sameth and Maximus trick him into crossing paths with a vampiric elf, thus transforming Jurgen into the vampire he is today. They do not find the Toybox in his cabin and Jurgen laments both his vampiric state and having failed Yog-Soggoth.
Jurgen makes a final appearance in "The City that Dares Not Sleep" working as Satan's cameraman while Satan delivers a report on how Max's transformation into "Junior" Max was not his fault.