The Ymir (ユミール, Yumīru?), also known as the Whelk, is a recurring creature in the Final Fantasy series, first appearing in Final Fantasy VI. It appears as a giant snail with powerful lightning-elemental abilities.
Appearances
Final Fantasy VI
The Ymir, also known as the Whelk, appears as the first boss of the game, encountered by Terra, Biggs, and Wedge in the Narshe Mines. Both its head and shell can be targeted, though only one needs to be defeated. Its shell is much tougher and will counter any attacks with the powerful Megavolt, but is otherwise completely passive. However, the head will occasionally withdraw into the shell, causing incoming attacks to redirect into the shell and triggering Megavolt.
Final Fantasy XIV
The Ymir appears as a family of wavekin, most commonly encountered in the Ruby Sea and its environs. Both shelled and unshelled varieties can be found. The common Ymir is first encountered as a boss in 
Hullbreaker Isle (Hard).
Final Fantasy Dimensions II
The Ymir appears as a wind-elemental eidolon obtainable by Parai. It teaches the Reflect Guard ability and uses Guard Breath when summoned.
Dissidia Final Fantasy Opera Omnia
The Ymir appears as a recurring boss first encountered in Act 2 Chapter 7.
Pictlogica Final Fantasy
The Ymir from Final Fantasy VI appears as a boss.
Final Fantasy Airborne Brigade
This section about an enemy in Final Fantasy Airborne Brigade is empty or needs to be expanded. You can help the Final Fantasy Wiki by expanding it.
Final Fantasy Record Keeper
The Ymir from Final Fantasy VI appears as a boss.
Final Fantasy Brave Exvius
The Ymir appears as a boss encountered in the "Scorn of Ymir" trial. Like the VI version, it has two targetable parts, the body and the shell. The shell has massive defenses and will protect the body from incoming damage, but can be broken to greatly reduce its defenses; destroying the shell is essential to defeat the body.
Mobius Final Fantasy
The Ymir from Final Fantasy VI appears as a light-elemental Monk ability card, granting the 10,000 Volts ability.
Etymology
In Norse mythology, Ymir is the father of the race of giants and the grandfather of Odin, King of the Gods.