Bugbear Shock Troop

Brute. A melee weapon deals one extra die of its damage when the bugbear hits with it (included in the attack).
Surprise Attack. If the bugbear surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 7 (2d6) damage from the attack.
Great Weapon Specialist. The bugbear may re-roll any 1's rolled for weapon damage when using a two-handed heavy weapon. Each die may only be re-rolled once.

Multiattack. The bugbear makes two melee attacks when it takes the Attack action.

Maul. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 15 (3d6 + 4) bludgeoning damage.

Breach the line. The bugbear forgoes multiattack for this action. The bugbear makes a daring attempt to completely crush a single enemy with a brutal swing of its maul. The bugbear gains advantage on a single melee attack against this target, and triple the number of damage dice are rolled. The bugbear suffers a level of exhaustion for doing this, and all melee attacks and melee spell attacks have advantage on the bugbear until the start of its next turn.
Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 35 (9d6+4) bludgeoning damage.