Mercurial

Change Shape (concentrate, polymorph, primal) — The mercurial takes on the appearance of any Small or Medium humanoid. This transformation allows for significant detail and can reproduce the features of a specific individual, but the mercurial retains a shiny, liquid-metal appearance that renders the transformation unsuitable as a disguise unless they're impersonating another mercurial. It doesn't change the mercurial's Speed or the attack and damage bonuses of their Strikes, but it does allow them to transform their limbs into metal tools or melee weapons, potentially changing the damage type dealt by their Strikes.

The monster changes its shape indefinitely. It can use this action again to return to its natural shape or adopt a new shape. Unless otherwise noted, a monster cannot use Change Shape to appear as a specific individual. Using Change Shape counts as creating a disguise for the Impersonate use of Deception. The monster's transformation automatically defeats Perception DCs to determine whether the creature is a member of the ancestry or creature type into which it transformed, and it gains a +4 status bonus to its Deception DC to prevent others from seeing through its disguise. Change Shape abilities specify what shapes the monster can adopt. The monster doesn't gain any special abilities of the new shape, only its physical form. For example, in each shape, it replaces its normal Speeds and Strikes, and might potentially change its senses or size. Any changes are listed in its stat block.

Metallurgic Adaptation (polymorph, primal) — The mercurial transmutes their liquid metal body into cold iron, copper, gold, iron, silver, or steel. Their unarmed melee Strikes are made of that material until they use Metallurgic Adaptation again.