In there you can only find zubat but the reason why its called the altering cave is because you can change what appears inside using a E reader device and E reader cards.
Nothing but zubat.
Firered don't have a "solar cave"
mewtwo is in mystery cave :D
It is in Cerulean Cave. It is on the bottom floor of the cave! :P
Four Island
Nothing.
altering cave,
cerluen cave
in the land cave.
Zubat.
cerulian cave
Cerulean Cave