Atomos is a boss in Final Fantasy V fought at the top of the Barrier Tower outside Castle Exdeath, where it is guarding it from intruders. Atomos is notorious for being a tough boss, becoming a summon in later games.
Atomos's main attack is Comet, which it keeps using until one of the team members is knocked out. Once someone is KO'd Atomos stops using Comet and starts drawing in the KO'd character. Once the character is close enough, Atomos will use Wormhole, removing them from the battle after which Atomos will start using Comet again until another member is KO'd. Rarely, Atomos casts Gravity, Graviga, Slow, and Slowga.
Speed is important here. Since Comet's damage does not factor in Defense, the party should not prioritize this stat. The best strategy is to let Atomos kill one character, then attack while Atomos is busy sucking them in. A White Mage should be constantly healing while the others attack with the best attacks and spells they have. Once somebody is KO'd, the White Mage should fully heal the other members while they continue to attack. If the White Mage is KO'd, it's best not to bother healing, and just focus on attacking.
Atomos is not immune to Sleep, so putting him to sleep and attacking him with spells can be a solution. Atomos won't stay asleep for long due to his Heavy status, but two Mystic Knights ready to use Sleep Spellblade works well. The Samurai's Mineuchi is the same as the Attack command without the drawback of removing Confuse, Control, or Sleep from enemies, and thus could also be combined with this strategy. For an even cheaper strategy, one can cast Dark Spark once, then Level 5 Death.
Another good strategy (particularly for a low level party) is to have a team of four Samurai—one Samurai should have access to Black Magic while another should have access to White Magic. After Atomos is put to Sleep (or let him kill a party member), the party should use Zeninage.
Other appearances Edit
Atomos is the Greek word meaning "indivisible" and is the the origin of the word "atom" which means "that which cannot be cut."