There are really only two main strategies. These are ordered from the easiest to hardest.
The best way (and usually easiest way) is to kill Odin using physical damage (Bow users preferred), and be careful with your healing in order to whittle down Odin's HP. There are a few recommended skills to bring.
First, you'll want to bring a normal healer, someone that uses Heal, Mega Heal, Giga Heal, or Tera Heal. A healer with Regen is not recommended, since you want to control when healing occurs. Heal, All works quite well, but there can be a lot of damage going out. Suggested characters include Sorman, Kuscah, Rikken, Zeera, Kana, R'zonand, and the SS healers. Control Time is also quite useful.
Second, a character who has Disarm Bomb, or using a Disarmer is highly recommended. After Odin uses Zantetsuso, everyone will be at 1 HP, and there will be 4 bombs around the arena. If placement is bad, characters tend to die to the bombs' explosion, or Odin's attack if heals aren't used. Odin can sometimes knock a character into bombs if unlucky. If damage is good, this is only needed one time, but if your damage isn't as good, you'll see this phase several times.
There are many characters who have Disarm Bomb.
Note that Blastosaur and Bomborg can be recruited through the story, and Blastosaur has more DEF than Bomborg.
Lastly, the rest of the team should be physical damage dealers. Characters with Phys Dmg x1.5 are recommended (S'naip, Ma'curi, Bahl, and Suoh). Since Odin is a spear type, bow units (Harold, Grace, Rikken, Camellia) will be able to do a lot of damage, and the two bow supporter units (Manmer with Augment Circle, and Pahrl with Atk+5%, and Desperate Measures) will be great as well. If you don't have many bow units, spear units (Bajanna, Yukken, Ra'prow, Djugan, Kem, and possibly Samatha [Job 2]), are good as well; they just don't get the damage bonus from the Circle of Carnage. Lastly, high damaging Sword units (Gugba, Zuzu) are okay, but they all take extra damage from most of the enemies. The sword supporter units, Ka'pori with both Augment and Negate Circle, and Korin with his Defense+20%/30% skills are very useful in keeping the sword units alive.
Some support-type units are useful too, such as Olber, Lunaken, Lunato, as they can provide evasion, but aren't as good in dealing damage. Olber can sometimes take a party member's hit from Zantetsuso because of Self-Sacrifice as well. Because most enemies Wild Beasts, Nakupi can be useful, but he is of sword-type. Ethereal is also a possibility, but it is weak, but can reduce Odin's defense to help out with damage for the team.
For the fight itself, kill off the minions in the first two turns; he will summon more on turn 7 even if any are still alive. Use a horizontal pincer on turn 1. If Odin used Breath Attack, decide if you want to pincer but get hit by Impair skills (and you'll have to use your power points), or avoid the Area (1) around Odin. If Odin used Thrust Away, then he'll use the Thrust Away (Cross) next, and make sure your pincering characters won't die from this next attack. After Odin uses Zantetsuto, clear the bombs with your Disarm Bomb user, and dodge the next Vertical (2) attack, and try not to heal at this phase. Like Turn 2, depending if Odin used Breath Attack, or Thrust Away, decide if you want to get hit by the following skills. If Impair Skills is coming and you have power points available for the next 3 turns, it's probably okay to get hit by Impair skills, but if Odin's going to use Thrust Away (Cross) next, either heal up, or dodge it completely. He will follow-up with Life Drain, and will heal himself based on how much HP your characters have left. If damage is good, you can kill him on this final turn. On his next turn, Odin will summon more enemies, and it'll be just like the first turn. Make sure to kill the adds as soon as possible, or they may kill you after the next Zantetsuto. Repeat until Odin is dead.
Much of this fight depends on how good your physical damage dealers are, as the faster the battle ends, the less mechanics you'll have to deal with.
Magic Defense -20%Edit
One farmable character, Red Starwhip (RSW), has this ability at level 30. This method is very frustrating and is not recommended for most people, but if you don't have access to characters with high physical damage, this is the only way to kill Odin without using Energy. RSW is a very fragile C-class monster and usually will die to anything. Also, in addition to RSW, you have to have a source of magic damage. A mage is preferred (such as Tiamat), but an elemental attacker can be substituted, but you'll have to be wary of skill activations to ensure Odin Omega dies at the right time. A healer with revive is recommended in case RSW dies on the way to Odin.
- On your first turn, you'll want to laterally double pincer Odin with Red Starwhip in the lineup; in addition, you'll want to chain RSW to a third pincer with the top right enemy, Draugr, as it doesn't counterattack. This gives Odin -60% Magic Defense. The other two minions should be ignored.
- On the second turn, you'll want to double pincer Odin and chain a mage to kill Odin after RSW applies its second debuff. The order of the pincers is important, because the mage (or elemental attacker) has to attack after RSW , or else it won't work. Typically this means that the mage isn't pincering Odin, and ideally the first pincer shouldn't involve RSW. If you're using an elemental attacker, RSW must pincer with your elemental attacker, and RSW has to be to the left (if laterally pincering) or on the bottom (if vertically pincering); and this pincer has to go second. (Older videos show that a triple pincer with RSW was necessary for the kill due to Odin's elemental resistance, but that is no longer the case since Patch 2.1.0.)
After five activations of RSW over two turns, Odin's Magic Defense will be 0, and any magical damage will cause effectively infinite damage. Before Patch 2.1.0 changed the rounding method of debuffs to favor the player, RSW needed to active six times for infinite damage, although it was possible to kill Odin in 5 activations with a lot of Magic Attack buffs.
In addition to a healer, RSW, and an elemental attacker, it is suggested to bring some physical damage dealers (bow-users preferred) to help kill enemies on the early floors, and to kill Hugin, and Munin on the final floor after Odin dies. These last two enemies will counter with a powerful attack as long as one of the other is still alive.
NOTE: with update 4.0.0, stat reduction skills will no longer reduce stats below 30% of the original stats. Hence this tactic is not a viable option anymore for an instakill.
- Therefore, Odin's MDEF can be reduced as low as 987.3 (30% of its original 3291 MDEF)