An Fenrisúlfr can use it’s action to go on all fours and increase it’s walking speed to 60, but decrease it’s swimming speed to 10. Climbing speed stay the same in either form
To stand on two legs, it must use a bonus action.

You can cast the Mage Hand cantrip at will.

Your dexterity score increases by two, and your constitution score increases by 1.

You go into a pure rage and bite a target within melee range. That target must succeed on a DC 15 dexterity saving throw or be poisoned. The target may repeat this saving throw at the end of each of their turns.

You have resistance to all nonmagical psychical damage.