Thirty Eight Island — Celia's Stupid Romhack
Every wild Pokémon here, by encounter method.
Thirty Eight Island lists 6 Pokémon across 5 encounter methods (grass, rock smash, old rod, good rod, and more), between level 5 and 35. One of them is on no other route's wild tables in this guide: Magnemite.
Opens up at Post-game. 1 trainer here: