Be even more hardcore: Fight the Elite Four with a single Pokemon at 1 health with no items at all.
BE EVEN MORE HARDCORE-R BY USING A SINGLE POKEMON WITH PERMANENT CONFUSION AT 1 HEALTH WITH NO ITEMS USING A LEVEL 1 MAGIKARP WHILE WHACKING YOUR HEAD AGAINST THE WALL SINGING I'M A LITTLE TEAPOT EATING A GIRAFFE
The Elite Four wasnt designed well. You can basically defeat them with Ghost Types
2 of the four to be exact with super effectiveness involved
unless you count the no effect of fighting which would mean... yeah you can defeat them all with a ghost pokemon.