User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-124.180.24.7-20121226065421/@comment-1837917-20121226082206

Everything but Subs, Zinogre, Nargacuga, Plesioth, Brachydios, Deviljho, Alatreon and Guran (obviously in those cases) are available in Low Rank. Once you transition to High Rank, you can take on Plesioth, Nargacuga and Zinogre, and all the Subs from Portable 3rd become available (par Green Narga), along with the addition of White Lagiacrus.

G-Rank is where things get crazy. Upon entering G-Rank, you can hunt Green Plesioth and Rust Duramboros. G2, you can take on Green Narga and Stygian Zinogre (dunno why Green Narga gets special treatment). G3 is where the Rare Species are located, as they are unlocked after defeating Guran.