In the spin-off game Pokémon Ultra Fire Red XD, Phantash has a Mega Evolution that turns it into a Flying type. Its canonicity is debatable however, as the events of the game take place inside of Kanye's mind.
The Phantash line is the only Pokémon line to completely change its type each time it evolves.
Phantash and its evolution line are the only Pokemon to be both in the Grass and Mineral Egg Groups.
The Sapleaf line came from the lack of Grass, Fire, and Ghost type representation in the dex. A joke post was made were an anon suggested that there should be a line that starts out as a pure Grass type, evolves into a pure Fire type and evolves again to a pure Ghost type to fix this. This was of course taken seriously. Quite obviously its design is how Sapleaf catch on fire, becoming Ignut, and turns to ash, Phantash.