Although Grovyle cannot learn flamethrower, there are other unexpected combos that can be taught through TMs and HMs such as Octillary learning Flamethrower. HMs, or hidden moves, can be used out of battle if you have enough gym badges or in battle. You can teach different pokemon these again and again. A TM, or tecnical machine is one use only. Flamethrower falls into this category.Normaly they are only usable in battle, but sometimes they can also be used ouside of battle, as is the case with Flash and Dig. You go in your bag and select the TM/HM section. Often it is represented with a disc. There you have a list of all of your HMs/TMs. You can select the one you want and press 'a' for more information about it. Then you can hit use. Every pokemon in your party will be marked with 'able' or unable' based on if they can learn the move. The pokemon you want to teach the move to, assuming they are able to learn it. If they have 3 or less moves, they simply learn it. If not, they must forget a move. You can obtain TMs by finding them, talking to people, or buying them at the department store. The same goes for HMs but they cannot be bought or sold.