I tried breeding my Venusaur with Petal Blizzard with my Trevenant to try to chain breed a Gourgeist with Petal Blizzard. Unfortunately, it seems that Trevenant cannot learn Petal Blizzard, so I'm gonna have to try other Pokemon. The only Pokemon with Petal Blizzard are in the Grass and Fairy egg groups, while Gourgeist is Amorphous. The only Grass/Amorphous is the Trevenant line (which, as I said above, cannot learn Petal Blizzard through breeding), while the only Fairy/Amorphous is Castform. In fact, the only Pokemon that are in Amorphous and another group are the Trevenant line, Castform, Stunfisk (Water 1), the Cofagrigus line (Mineral), and the Gastrodon line (Water 1). Unless any of these can learn Petal Blizzard through breeding, than it's out of the question for Gourgeist.