First of all head down to Dark Medows mansion and the security guard will spray you with pepper spay so you need to find some form of protection. Simply head down to Jimbo's gun store and buy the gask mask. Next return back to Dark Medows Mansion and talk to the security guard. He will spray you and then attack you so prepare to fight. Simply whoop his ass to complete the quest and have acess to the mansion. Once you have acess go to the manison and this is where you find token for cartman.