So, there are 12 different puzzles. They each take more pieces than the last one, with the first requiring only two and the 12th requiring 24.
Each puzzle yields something different upon completion:
Puzzle One: 2 Aging Points, 1 Daphne's Laurels, 1 Medusa's Blood
Puzzle Two: 1000 Equus, 10% energy for all horses, 1 Pandora's Box
Puzzle Three: Ow's Congratulations, 30 Apples, 1 Black Orchid
Puzzle Four: 5 Caloric Mashes, 1 Croesus' Fortune, 1 Helios' Ray
Puzzle Five: 5 Aging Pints, 1 Turnip, 1 Water Of Youth
Puzzle Six: 15 Energy Mashes, 100 Apples, 1 Golden Spurs
You get the pieces by grooming, opening HoPs, UFOs, winning comps, when you first log on and by watching a video.
The puzzles I have, so far, completed: (most of which are of Howrse horses on HR backgrounds..."