Boxing Kangaroo

Grappler. The Kangaroo has advantage on grappling checks, and when it grapples a creature, that creature is considered restrained by its tail. 

Iron Chin. The Kangaroo's AC equals 10 + Dexterity modifier + Constitution modifier.

Multiattack. The kangaroo makes two pummel attacks. Alternatively, it can choose to switch pummel attacks for a grapple attack.

Pummel. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) bludgeoning damage.

Flurry of Blows. The Kangaroo can make two additional Pummel attacks if they took the attack action this turn.

Aggressive. As a bonus action, the kangaroo can move up to its speed toward a hostile creature that it can see.

Second Wind(1/Short Rest). As a bonus action, the kangaroo recovers 8 (1d10+3) HP.

Sentinel. If the Kangaroo attacks a creature with an opportunity attack, the creature’s speed becomes 0 for the rest of the turn.

Additionally, creatures provoke an attack of opportunity even if they disengage.

Riposte. If a melee attack misses the Kangaroo, as a reaction, it can make a single pummel attack on the attacker.