Keen Smell. The bear has advantage on Wisdom (Perception) checks that rely on smell.

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.

Multiattack. The bear makes two attacks: one with its bite and one with its claws.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) piercing damage.

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 7 (2d4 + 2) slashing damage.

Slam. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage.