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

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

Pounce. If the thundermane moves at least 20 feet straight toward a creature and then hits it with a claw attack on the same turn, that target must succeed on a DC 13 Strength saving throw or be knocked prone. If the target is  prone, the thundermane can make one bite attack against it as a bonus action.

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

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 10 (1d10 + 5) piercing damage and 3 (1d6) lightning damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) slashing damage and 3 (1d6) lightning damage.

Cycle. If a spell is cast and has a cycle effect, or if there is a wildmagic surge the thundermane can use its reaction to deal 11 (2d10) lightning damage to a target within 120 ft.. The thundermane recovers life equal to the amount of damage dealt this way.