It was just easier to use your catagories.
Im not sure about some FG´s whether they are "Hard" or "Really Hard", but I would categorize them approximately like this:
Easy:
Divine Glory
Miracle
Destiny
Seism
Paradox
(Seldom losing due to a really bad draw.
Medium:
Fire Queen (Sometimes losing by not drawing Electrocutor, FFQ)
Osiris (Losing by not drawing Electrocutor, Pharaos)
Elidnis (Sometimes losing by not drawing Electrocutor, ForestSpectre)
Incarnate (Sometimes losing by not drawing Electrocutor; Retrovirus)
Chaos Lord (Survive the start or lose.)
Hard:
Decay (If he does not fractal your RoL´s you will lose. But even if he fractals your RoL´s its still hard. He can use DrainLife´s to kill you or at least to survive until you deck out.)
Rainbow (I think he is pretty tough and its even hard not leave, just because he needs hours for one turn later.)
Morte (Almost the same as Incarnate, but with Plague in addition.)
Neptune (Winning by early Flooding, but only 3 or 4 Tower, by not drawing Flooding, by having some luck.)
Dark Matter (Fast win possible by copying Archangels + some luck.)
Really Hard:
Obliterator (Momentum + permcontrol)
Gemini (PhaseShield + Momentumed PhaseRecluse, TU-Rush)
Dream Catcher (Almost same as ChaosLord. Survive the start or lose, although its much harder to survive.)
Ferox (You can only win if you are really fast at the start or Ferox doesnt draw more than about 4 FeralBonds.)
Graviton (Momentum + ablaze + permcontrol + Fire Storm)
Scorpio (Much poison + lobo + permafrost. Without early Electrocutor even 6 SoG´s wont heal you.)
Eternal Phoenix (FireStorms + perm control + small deck)
Probably Unbeatable:
Octane
Hermes