Phantastico is the mountain inhabited by the dreaded Phanfasms.
Description[]
A lava-filled gully encircles Mount Phantastico, about a third of the way up. Fire-serpents and poisonous salamanders live in it, and the heat and poisonous smell are so unbearable that even birds circle around the mountain rather than flying over it. A narrow bridge spans the gully and is guarded by a scarlet crocodile.
Beyond the gully, the mountain appears wild. The rocks are shaped like frightful beings and the tree trunks are gnarled and twisted like serpents. At the top is a level plain with heaps of rock in which the Phanfasms dwell. This is all an enchantment of the Phanfasms; they actually live in one of the most splendid and luxurious cities ever built by magic power. (The Emerald City of Oz)
Non-Canon[]
Petra on Phantastico.
Ruggedo and his companions visit Mount Phantastico. (Ruggedo in Oz)
Button-Bright also pays it a visit in Paul Dana's The Lost Boy of Oz.
Petra visits Phantastico to rescue her brother, Cutter, who was raised as a Phanfasm. (Emerald City Confidential)