"This highly sought-after ingredient can only be obtained from a Lynel. It pulses with the vitality of a Lynel, a strength that makes it invaluable as an ingredient for elixirs."
— In-game description

Lynel Guts are an item from The Legend of Zelda: Breath of the Wild. They are rare monster parts dropped by Lynels when defeated. Its description reveals it is a highly sought-after ingredient that pulses with the vitality of a Lynel, strength that makes it invaluable as an ingredient for elixirs. However they are even more valuable for upgrading certain pieces of Armor.

Link can cook with them and critters to make high-quality elixirs. If cooked by itself or with other incompatible ingredients, it will result in Dubious Food which is wasteful for such a valuable material. It is required by Great Fairies to upgrade the final tier of the Soldier's Helm, Armor, Greaves set, the final tier of the Radiant armor set, and the Barbarian Helm, Armor and Leg Wraps set. As a result, Link should save them for upgrades and avoid using them in creating elixirs until after upgrading to each armor's final tier.

Kilton at the Fang and Bone will give Link Mon in exchange Lynel Guts. Lynel Guts are worth 100 Mon apiece making them the most valuable Monster Part though Giant Ancient Core are worth the same amount and certain Dragon Parts are worth more Mon. However they are among the rarest Lynel drop and become harder to obtain as Silver Lynels start to appear thus Link should avoid selling them until he has acquired all relevant upgrades.

See also