They are a side quest. There are 28 unknown in total, one for each letter for the alphabet, an exclamation mark ('!') and a question mark ('?'). Once you have each and every one, a Pokemon will be unlocked depending our your starter Pokemon:
Bulbasaur -> Entei
Squirtle -> Raikou
Charmander -> Suicune
These Pokemon will be found randomly in the wild anywhere in the world. After you catch ALL of the unknowns, don't bother looking for the new Pokemon, instead, continue on with the game. You'll see it eventually. Remember, if you kill this Pokemon, you will NEVER see it again.
Actually, you do not need to get all the unknowns to get rakiou entei or suicune. i only have five but i have already found and caught rakou
Trade from Leafgreen or Firered.
go to 7 island
i think its unknown but im not sure... >.<
Unknown Dungeon was the name of a cave in Red, Blue and Yellow version that is located northwest of Cerulean City you would need Surf to reach their the cave is now called Cerulean Cave.
Firered and leafgreen both can catch different Pokemon but there pokedex is the same, here is some examples: magmar only in leafgreen not firered, oddish in firered not leafgreen, ekans in firered not leafgreen, bellsprout in leafgreen not firered, pinsir in leafgreen not firered.
what the pooperscoopers is the unknown dungeon in Pokemon firered you dummies?!
7island
Trade from Leafgreen or Firered.
the unknown M is in the rixy chamber
THEY DONT EVOLVE
go to 7 island
If you mean Unkown as in the pokemon, you can't.
U go to the Sucfib Chamber
Keep looking, you'll find it!!!
i think its unknown but im not sure... >.<
All 28 Unown are available in Pokémon FireRed within the Tanoby Ruins on 7 Island.
nothing happens unfortunetly