Originally Posted by
Camiie
I'm sure for Meteor you'll have to defeat Absolute Virtue or King Behemoth 500 times.
For Cait Sith I'm guessing you'll have to beat the WotG storyline along with all 3 past nation questlines. Then you'll get a quest where you have to farm up a bunch of items to get an NPC to craft another item that may not turn out to be suitable. If not, you have to farm it up again. Then you'll have to face off against an army of Cait Siths in a BCNM that will require 18 people. When you win you'll get an avatar that even though it essentially requires you to be level 99, it will be comparable in power to the avatar you received with your SMN at level 1 for reasons of BALANCE!!
Atomos will be obtainable by completing all wotg missions and nation quests. You will have to farm some relatively common new drop off of past Beastmen. You will then participate in a battle with up to 5 other people against Atomos. Atomos will then be useable during Astral Flow. He will have a low chance to "lure all enemies into an eternal time warp" if that fails however, the effect will be Dispel instead.