The four pieces of the Horny Talisman can be found in the following levels of the campaign:
In these levels can be found a Locate Hidden Land special. But if you do not get the special, you still recieve the quarter of the Horny Talisman.
When you have all the four parts of the Talisman, you can cast the Summon Horny spell. The cost is 100.000 mana, and Horny requieres 2.000 per game-turn to sustain himself in your realm. If you cannot pay this 2.000 mana, then Horny leaves.