Only one of the two parts need to be defeated. The head is the easier part to kill, but every ten seconds it hides in the shell and becomes immune to damage until it reappears. The head attacks with a physical attack and Slime, which inflicts Slow on a character. Attacking the shell prompts it to counter with Megavolt, which will take a large chunk of HP from the entire party. Ymir can use Megavolt six times before it runs out of MP.
It is best to not attack the shell and focus on the head. While the head is out, Biggs and Wedge should use any elemental Magitek beams and Terra should use Magitek Missile. While the head is hiding, the party should use Healing Force and wait until the head reveals itself.
A strategy for a fast victory is to keep using Terra's Magitek Missile without letting the soldiers attack. With luck, the creature will die before it can retract its head.
Ymir appears as a boss in the dungeon "Hullbreaker Island (Hard)", introduced in patch 3.3. In this incarnation, Ymir is able to switch its element between lightning and ice by switching its shell. Several weaker, slug-like versions of the monster called "Ymir Unshelled" appear as regular enemies in the same dungeon.
Ymir appears as a boss in Final Fantasy Record Keeper.
Defeat Ymir without being countered
Rush*Unofficial name: Standard attack
"Grawwwk...": Retreat into shell, or return to battle
Slime: Damage and Slow a target
Megavolt (Counter): Shell discharges Lightning against all targets
Players likely will have figured out the pattern from the previous two SNES-era bosses: attack, wait, attack, wait, repeat. This boss, however, hits about twice as hard, a fact made worse by its tendency to Slow its target. Ymir doesn't have any particular weaknesses. The player should again time the party's attacks while avoiding a direct hit on the shell and the resulting Megavolt retaliation, curing when needed. The pattern isn't hard to follow, but the fight could be a long one. Keep the pressure up and the rhythm steady for the win.
[view·edit·purge]In Norse mythology, Ymir is the father of the race of giants and the grandfather of Odin, King of the Gods.
It has also been known as Whelk and Biggs and Wedge call it "lightning whelk". [view·edit·purge]The lightning whelk is an edible species of large predatory sea snail or whelk, a marine gastropod mollusc in the family Buccinidae, the busycon whelks.