The Pigasus is a epic gear store located in Secret Lair, and to access it you need to use 5 different essences to summon him.
The store is vanished each time you leave Secret Lair, and 3 different gears are offered for each summon.
To find him, just go noth and click on room in the left, as appears in the image below:



Note: The gear available are all level 100 and costs millions of gold, good luck!