If you are having trouble beating Calasmos, this is what I wrote for the walkthrough. let's take out Calasmos.
, then play the flute and go to the dark star over Gallopolis.Calasmos
HP 11,000 (main body) MP Infinite Attack 720 Defense 520 Agility 320
No elemental resistances or Weaknesses
The trick to beating Calasmos is to use the Super Sword of Light (not the Supreme Sword) as an item in battle. Have it in the Hero's inventory, and select "item" on his turn, then use the Super Sword of Light. Doing so strips Calasmos of his dark aura and making him much weaker. He takes more damage, and attacks less often and for less damage. Once you know this trick and are level 99, this fight is easy.
I brought Hero, Hendrick (greatsword), Jade (claws) and Serena to this fight. Don't bother with attacking Calasmos's arms, they each have 5,000 HP, so you could nearly kill him just as fast. When he summons Darklings to pray to him, kill the darklings fast. Hero's Quadrasword and Jades multifeet should take them out. Calasmos knows disruptive wave (as will nearly all bosses after him) which removes pep as well as any buffs on the party. Use your pep powers as soon as the party can to avoid losing pep. The most dangerous power of Calasmos is stop time, which leave just him fighting one party member. This can be deadly for the single party member, but with Hero, Hendrick and Serena all knowing Kazing, you can rescue whoever he kills. If he confuses or puts to sleep someone other than the Hero, have the Hero use the Supreme Sword of Light to remove negative conditions. The other dangerous move Calasmos knows is a final fireball. This will give you a few turns to prepare. Have Serena use Grace of the Goddess, then Hymn of Fire, while the Hero uses Omniheal. and your party should survive.
There are a few strategy guides for beating Calasmos in as little as two moves, but those usually require more prep work before the big fight. It's a net time waste. Just focus on hitting him hard and staying healed and you'll be fine. One quick strategy if you have trouble is:
1: Pep all party members before the fight. Bring Hero, Hendrick, Veronica and Serena.
2: Hero uses the Super Sword of Light as an item.
3: Veronica and Serena use mighty magic burst pep power to deal over 5000 damage, taking out both arms.
4: Hendrick and Hero use Elfin Elixirs (from the casino) to restore the girls' MP
5: Which whichever girl acts first uses a pep pop (from the store in Cobblestone) to restore pep to the party.
6: Veronica and Serena use mighty magic burst pep power again. Calasmos has no arms and less than 1000 hp.
The only problem with this strategy is that you should save your Elfin Elixirs and Pep Pops for the real final boss, Timewyrm.
Once you beat Calasmos, A cutscene will return you to Cobblestone. Everyone is celebrating. Head North and talk to Veronica and Serena. Say Yes, you do want to return the Sword of Light to Yggdrasil. There will be a cutscene, walk forward to the Heart of Yggdrasil and return the sword to unlock