Brute. A melee attack 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.

Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 9 (2d6 + 2) piercing damage.

Throw Goo. (1/Day) The zombie hurls a ball of infectious goo that explodes at a point it can see within 30 feet. Each creature in a 10-foot radius sphere centered on that point must make a  DC 15 Dexterity saving throw. A creature takes 4 (1d6) poison damage plus 4 (1d6) necrotic damage on a failed save or half as much damage on a successful one.