This question is being asked shortly after this one https://pokemondb.net/pokebase/289641/how-does-seismic-toss-work-in-gen-1?show=289642#a289642. So I accidentally caught myself in a soft-lock when fighting Koga when I found out my team is too underleveled for Koga. I tried grinding but the process is way too slow. What is the fastest way to grind in gen 1? Discluding the Exp. All of course.
Another tip: Use Psychic, Ground, and even Fire, Rock, and Flying-types to get the best out of defeating Koga, as all of his Pokemon are of the Poison-type, including some Bugs.
Source: Experience and knowledge