In the Fire red and Leaf green games (like in many others), the Unowns are present. This time, in the Sevii islands. After solving the puzzle from the Tanoby Key, Unown will begin to appear in the Tanoby Chambers. There's seven of these chambers: the Monean Chamber (Unowns A, and ?), the Liptoo Chamber (Unowns C, D, H, U, and O), Weepth Chamber (Unowns N, S, I, and E), the Dilford Chamber (Unowns P, J, L, R, and Q), the Scufib Chamber (Unowns Y, G, T, F, and K), the Rixy Chamber (Unowns V, W, X, B, and M), and the Viapois Chamber (Unowns Z, and !).

The Unowns located in the Tanoby ruins have a peculiarity that makes them special. As you may know, the full odds in Fire red and Leaf green are normally 1 in 8192, but these Unown are an exception to this. Depending on your TID (trainer ID) and SID (secret ID), the shiny odds for these Pokémon will be different depending on the letter. These odds can go as high as 1 in 5120, and as low as 1 in 18432. As you can see, you can unknowingly be trying to shiny hunt an Unown with difficult odds. Or maybe those 30 thousand encounters you did may have an explanation after all. Eitherway, with this calculator you will be able to find the odds of your save file. If you want a more in-depth explanation of how this works, you can check the original post (in french). Credits to Redac' Angeflo for the original research of all of this.