You Use Darkrai Or Diagla Or Palkia Or if you wan't to be a noob use Acreus =P that's how i did it =P
There is no altering cave in pookemon red since the sevii islands don't exist in Pokemon red only in Pokemon firered and leafgreen in six island after going past the forest and the altering cave is also in Pokemon emerald in route 103 a cave appears after beating the elite 4.
you throw an apple at the voltorb near the rocks , at the end of the cave , to get the apples you have to take pictures of Pokemon after the cave level
You need to have a national dex and need to have caught 70 or 110 pokemon.(I don't remember the exact number and whether you have to see or catch these number of pokemons but I am sure you have to do all these to get past the cave.You will get a Mewtwo in there).
Go to the right of Azalea town past the cave with the slowpoke once you head down past that you should see a cave it will say route 33 this is union cave
to get him to move you have to beat Team Rocket inside the cave on four isand first
Just past victory cave
you go past the moon cave.
Past the cave to the west of cainwood city.
Go through the cave
You push boulders into a bunch of holes to stop the flow of water (you need strenth)
You don't. Go get an electric pokemon.
go to the hideout, the opening in that cave north of the wailmer