I'll base my answer on Island Kahunas.
Typhlosion is not good against the 2nd and 4th Kahunas, so don't use it. It doesn't have any good fighting moves that can capitalize on its good special attack stat, except for focus blast. Plus, you're pretty much screwed if you miss or don't one shot. You can get solar beam, but you have to set up sun to make it really work, which means running specific Pokemon and surviving a switch in. Not very reliable.
Feraligatr has no weakness to the kahunas, and it hard counters the 2nd and 4th ones. However, you only get a good physical water move on Poni Island if you don't use breeding, so it is better to get a aqua jet Totodile from breeding, if you are okay with the grind. Go here(https://pokemondb.net/pokedex/feraligatr/moves/7#egg-move-parents) and scroll to the aqua jet section.(also please teach me how to link a URL in a word, I don't know how to do it currently)
Meganium is the best, in my opinion. It is reasonably tanky. Even as a Chikorita it gets good grass moves early on. It can also comfortably take a z-move from the rock and ground Kahunas, so it is a good defensive and offensive option.
Hope I helped!