Giving a lot of information because it is important to the thought process.
There are a few Pokemon that cannot be taught TMs: Caterpie, Metapod, Weedle, Kakuna, Magikarp, Ditto, Unown, Wobbuffet, Smeargle, Wurmple, Silcoon, Cascoon, Wynaut, Beldum, Kricketot, Burmy, Combee, Tynamo
There are a few TMs that can be learned by every Pokemon besides those listed above: Toxic, Hidden Power, Protect, Frustration, Return, Double Team, Facade, Rest, Atrract, Round, Swagger, Substitute
Unown and Burmy can learn from level up one of the above moves: Hidden Power.
This means Hidden Power is the move learned by the most Pokemon.
