Originally Posted by Artificial Hallucination
The northern Cave is the North Crater. It's the final area of the game and is a little hard to miss.
The Magic Pots themselves are in a specific area of the Crater.
The first time you have to split your party choose to go left. At the next junction choose the route towards the top of the screen, or the north.
You will find yourself in a swamp-like area with lots of earthy brown colours and lots of weeds or vines snaking through water; the Magic Pots can be found here.
What you think they have to do with defeating Emerald WEAPON I can't fathom, the only notable features of these monsters are the facts that they are completely invulnerable until you give them an Elixir, after which you can kill them.
They do offer lots of AP, which is useful for advancing your Materia but, again, I don't see what this has to do with Emerald WEAPON.
Your theory about defeating Emerald with eight Mimes and eight Counters is a new one to me and I don't see how or why it could work.
I won't go into detail explaining how to defeat Emerald; but equipping so much materia would be a bad move.
Emerald's signature attack - Aire Tam Storm - does damaged based on the amount of materia you have equipped.
If a character has (for example) three Materia Aire Tam Storm will do 3333hp damage to that character, so you can see it's best to be as economical as possible with your Materia when attacking this WEAPON.