Full ability set, resistances and AI can be found on the Wiki.

Feel free to correct me if there are any wrong/misleading informations or some new tips that needs to be added.

Overview

Stats

• Race: Aquatic/Plant

• Can be fully broken

• Resistance:

AI Summary

(Fire/Thunder/Water/Wind/Earth will be referred to as preferred element.)

Weakness Count starts at 0, increases by 1 for each unique preferred element used. You can do all 5 in one turn (read: Tiana) or spread the usage throughout different turns.

• Ambush is ST and can be provoked and immuned with 100% light/ice/water resistance
• Permanently self-imperil all elements by 300% after Weakness Count reaches 5
• Boss will not set up mitigation after getting hit with one of the preferred element on 6 different turns OR not getting hit by any element the turn before
  
• Under 50% HP, reset Weakness Count and sets up mitigation until it reaches 5 again
• Retaliate ice/light/dark damage with 6 ST all element damage and AoE MP drain
• Dealing one of the preferred element every turn to avoid AoE imperil (can be sealed/reflected) morale penalty
• Other imperil is 200% ST, can be reflected (will trigger retaliation) or sealed.
• Turn 4, 9, 14,...: ST Paralyze & AoE Sleep
• Most other attacks are AoE ice/water/light, can be covered and resisted
• Ends turn with one basic attack w/ accuracy, survivable

Team Building (0 EX Modifier)

• Boss has lowest resistance to Lightning and Wind.
• Bring a source of fire, thunder, water, wind and earth damage.
• After buffs, provoker with 300% ice/water/light resistance team with 100% ice/water/light resistance will be able to ignore 99% of the damage.
  The 1% is the basic attack but doesn't require too much bulk.
• Reflect Ring owners can give it to their provoker and ignore the imperil entirely, though be prepared for AoE MP drain all element damage every turn.
• Tanks are not required at all, but a physical tank can be used to ease the resistance requirement on your provoker (only need water and light).
• Prepare Paralyze and Sleep resistance.
• Tiana will instantly get the Weakness Count to 5 with her BS LB.
• Keep Morale higher than 115% by turn 5.
• Earliest burst turn is turn 3 if you get Weakness Count to 5 on turn 1 and don't do any elemental damage on turn 2.
• You do not need to hit the boss with all 5 of the preferred elements every turn.