Here's the wiki and BG wiki pages for Atmas.

The first link has some stuff that someone newer to Abyssea might find interesting, such as stuff about Red !!'s. The second link probably has more accurate values for some of the Atma, however.

Abyssite are also important. They're key items that have less drastic effects (other than the three that allow Atma to be equipped) but you always have them with you. Here are the wiki and BG wiki pages for Abyssite.

Looking at those pages, you can see what's what for yourself way better than I could tell you.

Now, as far as which of those thingies are actually good, lots are situational. There are a few that really stand out, though.

First and foremost, you want at least one Lunar Abyssite and Minnikin Monstrosity. It has a very, very potent Refresh effect that will allow a White Mage to cure whatever horrid things happen to almost-atma-less melee while working on other Abyssites and atma.

After that, the other two Lunar Abyssite and Atma of the Razed Ruin are also important but probably not as important as Minnikin Monstrosity since it helps people make people not die. It also helps that the series of Notorious Monsters needed for it are pretty weak.

Keep in mind that there are Abyssite which add to your maximum HP/MP, and these are also important. Most are easy to obtain, a few are not.

As for how to kill the things...uh...grab some friends and reduce their HP to zero is all I can say. I can't imagine the monsters in Visions and Scars areas being that hard for a group at level 95 or 99 even without many Abyssea-specific buffs.

Once you guys get into the feel of things and collect a few Atma and Abyssite, things will hopefully feel much more smooth. Good luck!

Also, here's a robot offering his advice:



I have no idea what he is saying, but I assume it is as horrifying as he looks.