Keen Smell. Abbadon has an advantage on Wisdom (Perception) checks that rely on smell.

Pack Tactics. Abbadon has an advantage on an attack roll against a creature if at least one of the its allies is within 5 feet of the creature and the ally isn't incapacitated.

Abbadon can make two attacks:

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 10 (6d6 + 6) piercing damage.

Baby Rattle Mace Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 16 (8d8 + 8) bludgeoning damage.

 Rampage. Abbadon goes into a frenzy and rampages through the battlefield. For the duration of the rampage, the base speed is double, the baby rolls a d100 and the action is based on the chart below. The rampage lasts for 3 rounds. When the baby's Rampage ends, it suffers one level of exhaustion.

D100 Rampage Chart:

1-10: Hideous Laughter: The thrill of battle consumes Abbadon with happiness; He lets out a burst of hideous laughter Tasha's Hideous Laughter. Every creature must succeed on a Constitution (DC 18) saving throw or fail.  

11-20: Abbadon Farts: Abbadon has uncontrollable bowel movements and creates a 20-foot-radius sphere of yellow, nauseating gas centered on a point within range. The cloud spreads around corners, and its area is heavily obscured. The cloud lingers in the air for the duration. -Each creature that is completely within the cloud at the start of its turn must make a Constitution saving throw(DC18) against poison. On a failed save, the creature spends its action on that turn, retching and reeling. Creatures that don't need to breathe or are immune to poison automatically succeed on this saving throw. -A moderate wind (at least 10 miles per hour) disperses the cloud after 4 rounds. A strong wind (at least 20 miles per hour) disperses it after 1 round.

21-30: Baby Rattle Mace Melee Weapon Attack: +5 to hit, reach 15 ft., one target. Hit: 10 (10d8 + 8) bludgeoning damage.

41-50: Teenager Breath (Recharge 5–6). Abbadon exhales Acid in a 30--foot cone. Each creature in that area must make a DC 18 Dexterity saving throw, taking (10d6+6) acid damage on a failed save, or half as much damage on a successful one. 

 51-60: In the Zone: Abbadon becomes extremely focused during the battle and begins to emanate an Aura of Protection for all allies within a 30-foot radius

61-70: Blind Fury: Abbadon goes into a blind fury, striking out at every creature within reach. Use the Baby Rattle Mace for Damage.

71-80: Disarm: Abbadon will attempt to disarm the first opponent it sees within reach. Abbadon makes an attack roll (at advantage) contested by the target’s Strength (Athletics) check or Dexterity (Acrobatics) check. If the baby wins the contest, the attack causes no damage or other ill effect, but the defender drops the item.

81-90: Teleport: Abbadon's instincts kick in and he teleports up to 60 feet away to gain an advantage in battle

91-100: Fireball: A bright streak emanates from the baby engulfing anything within range, and then blossoms with a low roar into an explosion of flame. Each creature in a 30-foot-radius sphere centered on the baby must make a Dexterity saving throw(DC18). A target takes 14d6+8 fire damage on a failed, save or half as much damage on a successful one. -The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried.