In the cave, when they are sleeping, Cartman behaves just like Humphrey Bogart's delusional and greedy character in The Treasure of the Sierra Madre.
movie poster in Stan's room
Al Gore says the cave must be filled with molten lead to kill Manbearpig; the Alien in Alien³ was killed this way.
Manbearpig attacks Imaginationland.
Manbearpig is in Imaginationland; Al Gore re-appears.
Al Gore and ManBearPig make a re-appearance
Cartman acts like Bogart's character when he discovers treasure, Cartman talks to sleeping Kyle and he wakes up and wonders what Cartman is doing
The sequence in which Al Gore "stalks" the boys while dressed as ManBearPig references the 1977 movie Snowbeast, which features similar music and presentation to that segment. The tagline reads "The legendary creature is half man... half animal... and a cold blooded killer!" which is similar to how the ManBearPig is described.
Al Gore constantly misusing the word "serial" is a parody of the time he confused it with "cereal" on Oprah
Al Gore quotes from this movie mimicked