Change Appearance. Riley can use their action to turn their skin into bark and change their teeth into numerous sharp, elongated needles. While in this form, Riley's AC becomes 16 if they aren't wearing armor, Riley may use their bite attack, and Riley has disadvantage on all Charisma checks.

Attacker. Riley gains +2 bonus to all attack rolls (already factored in to their listed attacks).

Improved Critical. Riley's attacks score a critical hit on a roll of 19 or 20 on the d20.

Multiattack. Riley makes one attack with their scimitar and one attack with their bite..

Scimitar. Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 7 (1d6 + 3) [slashing] damage. 

 Bite (only when polymorphed). Melee Attack: +8 to hit, reach 5 ft., 1 target. Hit: 3 (1d6-1) [piercing] damage. On a hit, the target must succeed on a DC 14 Constitution saving throw or have disadvantage on the next attack roll it makes before the start of Riley's next turn. 

Second Wind. Riley can use a bonus action on their turn to regain hitpoints equal to 1d10 + his CR. Once Liam uses this feature, they must finish a short or long rest before they can use it again. At 20th level, Liam can use this feature twice between rests.