A famous Amiga demo from the Finnish (and Swedish) division of Scoopex.

Mental Hangover was released in April 1990 at the Swedish Elite Easter Conference held in Göteborg, Sweden. It won the demo competition, earning the creators a 14.4k modem as the first prize.

The demo is considered to be the first trackmo ever created. Until its release, demos had taken the form of small one-part intros or megademos, which were basicially small intros joined together by a loading screen. In a full-disk trackmo, the next effect/part is loaded into RAM while the previous one is still playing, creating a fluid and less fragmented presentation. The claim of Mental Hangover being the first trackmo ever - or one at all - has been debated over time, but generally accepted as the truth. In any case, it was definitely very influental for the entire scene.

Not that the demo in question wouldn't have other merits as well. The code by the most famous Finnish demo programmer of all time, Slayer, features many original effects along with ones greatly improved from prior creations. Great graphics by Reward and the insane soundtrack "Madness Took Me" from the Swedish member Uncle Tom certainly helped in making Mental Hangover generally regarded as one of the most important pieces of scene history.

MH established the Finnish Scoopex members' place in the demo coding elite. Unfortunately, not counting the demo Chromium released in November 1990, the Slayer/Reward duo failed to release anything equaling, much less topping their breakthrough product. Slayer was soon called to serve in the Finnish Military, and after his long stay there he didn't have any interest in the scene anymore, and he more or less disappeared without a trace. Reward continued to be somewhat active, and even released his graphics on the PC as a member of Complex. He recently worked as the chief art director on the game Max Payne.

  Mental Hangover's Effects:

The authors' handles presented as plane vectors on the same moving starfield that can be seen behind most of the effects. Subsequently copied by numerous groups.
Filled Bobs
Small vectorbobs with Copper FX gradients on top of them. Not a record amount of bobs on screen, but Slayer's try at the "world record in insanity".
"Do you like filled vectors? We do!"
An another version of the previous effect, this time with big filled vector objects with the copper effect on them. Very pretty.
Stencil Vectors
Perhaps the most well known part of Mental Hangover. It's basicially texture mapping emulated by an extremely simple trick: Instead of filling the polygons with a single color, it is done with 2D bitmap patterns moving on the X and Y axels. Since their perspective and rotation don't change with the object's movement, the result looks quite weird and not like real texture mapping. Still, the effect was quite spectacular and original in spring 1990.
Rotating and twisting scrolltexts were nothing new at the time, but this 2-plane smooth-as-silk scroller looked ten times better than earlier similar effects from competiting groups. That, along with the text including gems like "only beer makes it possible", make this one of the memorable parts of Mental Hangover.
Filled Vector "Paranoimia" Scrolltext
An another fine example of Slayer's attitude. The effect improves on Paranoimia's classic crackintro with the blue line vector scroller in perspective. The coder isn't shy about this either, judging from the text. "Hey Paralamia and Unique, your quality is from the toilet!"
This part was later on used by itself as a Scoopex cracktro.
Fake-3D bobs bouncing on a color-shifting chessboard plane, along with the famous Scoopex slogan "Generations Ahead". No scrolltext, no "The End". The last part maintains the demo's general idea: straight to the point.
The demo is available as MPEG-4 in ftp://ftp.scene.org/pub/mirrors/amidemos/menthang.zip
However, if you have an old Amiga 500 in the closet, or a PC fast enough to run WinUAE properly, I'd suggest to get the real thing instead: http://amiga.emucamp.com/demos/countdown.cgi?mentalhangover.zip

Information from the demo itself, my own memory from the Amiga scene days and several old diskmags.
Some tidbits from http://exotica.fix.no/info/scenery/online/s.html
No cut'n'paste writeup. Happy nuking.