The Fusion Hexagram is a building that allows you to fuse 4 and 5 star monsters. You will have to sacrifice 4 lower grade monsters in order to get 1. Below are the required recipes that are available for players. All monsters used for fusion must be awakened.
These fusions do take quite a bit of work, but some are really worth it. My recommendations are:
Fire Sylph – A good speed leader and great AoE as well.
Water Phoenix – A good damage dealer, which the water element lacks.
Dark Ifrit – Ability to heal and remove harmful effects is too good to pass up.
Scroll down to see all Fusion Hexagram ingredient trees. We also have a fusion chart here.