Fact #75

Did you know that the move Megahorn is a Bug-type move, yet only four Bug-type Pokémon can learn it.

These Pokemon are Heracross, Scolipede, Karrablast and Spinarak. 

However, Karrablast can learn Megahorn if it breeds with a Heracross or Scolipede in Generation V

Spinarak can learn it by breeding with the same Pokémon as Karrablast, but it has to be in Generation VI