"Although it always pretends to be a tree, its composition appears more similar to rock than to vegetation."
Pokemon in the beginning rarely went for oxymorons in terms of having a Pokemon look like one thing, then being another. Sure, you had Slowpoke become a psychic type, but that was a rare case. With Johto, and Sudowoodo, they went full oxymoron. They made a Pokemon that looked like a tree...but was actually a Rock-type. This was actually a big point that they made in both the anime and the games as you had to use water to get rid of it in particular cases.
Sudowoodo's Basic Attacks are Rock Throw and Counter, while its Special Attacks are Stone Edge, Earthquake and Rock Slide.