Companion
It follows the hero, and what it gives never changes — no meals, no growth.
From Maelle the Tamer at the Tides, once you have gone down into the Leviathan’s Pit, in exchange for a Selkie Charm — it rarely falls from the creatures of those waters.
A mount or a companion — never both at once. Saddling a mount puts away your companion; taking out a companion unsaddles your mount.