Drogon, Adult Dragon

Drogon, Adult Dragon cannot be cast or put
into play unless Drogon, Hatchling is in your
graveyard or exiled.

Drogon, Adult Dragon and Daenerys
Targaryen gains flying, haste, trample, and
Ward - Sacrifice two creatures.
When Drogon, Adult Dragon dies, shuffle
Drogon, Adult Dragon and all dragon
creatures from your graveyard into
your library.