Armor Class 17 (natural armor)
Hit Points 22 (4d8 + 4)
Speed 30 ft.
Skills Athletics +4, Survival +3
Senses passive Perception 11
Languages Aquan, Common
Challenge 1/4
Hold Breath. The tortle can hold its breath for 1 hour.
Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) slashing damage.
Quarterstaff. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) bludgeoning damage, or 6 (1d8 + 2) bludgeoning damage if used with two hands.
Light Crossbow. Ranged Weapon Attack: +2 to hit, range 80/320 ft., one target. Hit: 4 (1d8) piercing damage.
Shell Defense. The tortle withdraws into its shell. Until it emerges, it gains a +4 bonus to AC and has advantage on Strength and Constitution saving throws. While in its shell, the tortle is prone, its speed is 0 and can't increase, it has disadvantage on Dexterity saving throws, it can't take reactions, and the only action it can take is a bonus action to emerge.
Mordenkainen's Tome of Foes, p. 242