Ultimate_charmander, get a Slugma.
Now, the way you can get a Slugma before you beat the Elite Four is somewhat complicated, so I'll explain. In Violet City's Pokčmon Center, there is a man to the right of the counter named Primo. If you give him a certain combination of words, he will give you a new background for your PC, or a Pokčmon egg. The three eggs he can give you are of Wooper, Mareep, and Slugma. The combination of words is different for each thing he can give you, and for each save file-- this is because the randomly-generated word combinations are based on your Trainer ID. To find out how to get the Slugma egg, just go to this page, enter your Trainer ID in the blank, and press "Send". Scroll down the page, and the words you need to get a Slugma are right there.
With that out of the way, now for the restrictions!
Your Slugma must be taught Fire Blast using a TM bought from the Goldenrod Departmant Store as soon as possible, and it must keep this move forever. In order to evolve, Slugma must use Fire Blast to burn at least three Pokčmon who resist Fire.