Pokémon Red Coast Pokémon

@SnorlaxMonster @djah15: There doesn't seem to be much research on this wider aspect of the coast glitch, so what I'm going to post is based on research that is empirical, but is not taken from the game code itself.

Only 'left-facing shore tiles' seem to allow for wild 'grass' Pokémon, but apparently (I haven't been able to encounter one in this situation) if you're in a location where there are no surf-obtainable Pokémon, including Cinnabar Island itself (not the east coast because that counts as Sea Route 20), Route 10 (where the Power Plant is) or Route 24 (Nugget Bridge), then you will never find a Pokémon on that shore.

'Right-facing' and 'horizontal' shore tiles seem to act differently than left-facing shore tiles. Horizontal ones seem to give you normal surf Pokémon, while right-facing ones don't seem to give you any Pokémon (this is an ostensible assumption as well), even if its from a route with wild Pokémon excluding rod Pokémon, i.e. Sea Route 21.

It's interesting that Twitch Plays Pokémon found a wild Rattata on Sea Route 21. It seems that the only 'left-facing shore tile' Pokémon you get on that route are those that are found in the grass (Rattata, Pidgeotto, Raticate, Tangela) and I suspect this is because Sea Route 21 has valid grass data.

It's possible to perform the coast trick in a Sea Route 19 Glitch City too, where coast tiles normally don't exist because that particular Glitch City has horizontal and left-facing shore tiles. I haven't tested whether you can find normal Surf Pokémon in the horizontal shore tiles there or not though. That would back up my hypothesis.