Alimighty. If the Brushwagg has the Enlarge (Enlarge/Reduce) spell cast on it, in addition to the spells effects the Brushwagg also gains the following effects. The Brushwagg gains +6 to its Strength score. It gains +2 to it's AC, and its hit point maximum and current hit points increase by 10 for the duration.

Keen Smell. The brushwagg has advantage on Wisdom (Perception) checks that rely on hearing or smell.

Prickly. A creature that touches the Brushwagg or hits it with a melee attack while within 5 feet of it takes 2 (1d4) piercing damage

Trample. If the Brushwagg reduces a creatures HP to 0 the brushwagg may make an attack as a bonus action.

Bite. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. Hit: 2 (1d6 - 1) piercing damage.

Enlarge (Recharge 5-6). The brushwagg grows as if the Enlarge/Reduce was cast on it. This causes the brushwaggs Almighty ability to activate.