Wind Weasel

Air Form (Whirlwind Form Only). The wind weasel can enter a hostile creature's space and stop there. It can move through a space as narrow as 1 inch wide without squeezing.

Flyby (Whirlwind Form Only). The wind weasel doesn't provoke an opportunity attack when it flies out of an enemy's reach.

Hidden In The Wind (Whirlwind Form Only). Until it attacks or uses Whirling Leaves, the wind weasel is indistinguishable from a natural dust devil unless a creature succeeds on a DC 15 Intelligence (Investigation) check.

Shapechanger. The wind weasel can use its action to polymorph into a whirlwind. It can revert back to its true form as a bonus action. It statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies. While a whirlwind, it has a flying speed of 60 feet, immunity to the grappled, petrified, restrained, and prone conditions, and resistance to bludgeoning, piercing, and slashing damage from nonmagical attacks. The wind weasel can't make bite or claw attacks while in whirlwind form.

Windy Speed (Whirlwind Form Only). When the wind weasel is subjected to the slow spell, it doesn't suffer the effects of the spell but instead is forced into its true form and incapacitated until the end of its next turn.

Multiattack. The wind weasel makes three attacks: one with its bite and two with its scythe claws.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) piercing damage.

Scythe Claw. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (1d10 + 3) slashing damage.

Whirling Leaves (Whirlwind Form Only). Each creature in the wind weasel's space must make a DC 13 Dexterity saving throw, taking 21 (6d6) slashing damage on a failed save, or half as much damage on a successful one.