A dark full moon night the childless Bulls find a crying baby on their stairs, while a dark hose carriage disappears, and decides to adopt him. But later they discover that their young son, christened Buffalo, is not like every other child.—OJT
An unhealthy-looking man sporting vampiric fangs bites a female taxi driver, causing the car to crash. We cut to his funeral, and then move back in time to cover his entire life-story leading up to his dramatic demise.
As a baby, he was left on the doorstep of a childless couple, who promptly took him in him as their own son. He was christened Buffalo Bull (sic). During his childhood he discovered a taste for blood, causing him to cut all of his fingers to suck blood from himself. When around twenty, he met and fell in love with a young lady called Svalbard (sic again), but at the same time he also claimed his first victim. After various mishaps involving his bloodlust (all played for laughter), he went berserk in a restaurant after tasting pizza with garlick on it, his embarassing behavior causing Svalbard to end their relationship. Years passed, and Buffalo Bull was eventually convinced by a doctor that his vampiric tendencies were just a relatively harmless delusion; he must simply isolate himself around full moon when his bloodlust would peak.
At this point he once again met Svalbard, who now regretted ending their relationship earlier. She invited him home and wanted to spend the night with him, but Buffalo excused himself, knowing that he would end up biting her. Shortly afterwards he attacked a taxi driver and was killed in the ensuing crash, as shown in the opening scenes.
The lengthy flashback covering most of the movie comes to an end, and we are back in the present, at Buffalo's funeral. Suddenly his coffin opens and he rises as a fully-fledged vampire (with deliberately overdone make-up to make him resemble Bela Lugosi's Dracula). Svalbard willingly joins him, and they escape in a horse-drawn carriage that appears out of nowhere, eluding the police. He takes her to a house, places her on a bed and uncovers her neck, and she does not resist as he is about to bite her (and posssibly make her his immortal companion). However, as he leans over, mouth wide open, his jaw suddenly snaps out of joint. Svalbard is able to help him, but Buffalo despairs when he feels like a failure even as a bona fide vampire. Even he who truly was and is "something completely different" (referencing movie title) wants to be something still different.
In the final scenes (where Buffalo has curiously been restored to a human appearance), he has apparently found his calling as a COMEDIEAN, but the bland jokes of his stand-up routine fail to amuse his audience in the slightest. However, the occasion is a jubilee of Norwegian bakers, to be celebrated with a cake so enormous that it has to be brought in by helicopter. The cables snap and the monster cake lands on Buffalo, finally making his audience laugh.