Beserker

Enraged Soul: Beserker is always in a rage state nothing can quell it except for the one who commands him (requires special ritual). Beserker also deal an extra +4 damage to hit targets with melee attacks. Beserker also had advantage on all strength skill checks and strength saving throws.

Pact of Heroes: While on this plain of existance Beserker has been summoned here through an ancient ritual thats been modified so that Beserker is always in a constant rage. If the one who summoned him is killed them Beserker will attack everyone in sight until everything is dead. It is possible to make a new pact with the Beserker but it extremely difficult and requires an ancient form of magic to perform.

12 Tasks of the Beserker: While in life Beserker was given 12 tasks to prove himself. Beserker did all 12 tasks so as a twisted addition to the ritual Beserker must be killed 12 times per time they are summoned. Beserker will resurrect in 1 day time.

Champion of the Summoner. Beserker Critical hits on 19 - 20

Brutal Critical. When Beserker gets a critical hit he can add 3 weapon damage dice when determining damage from a critical hit.

Beserker Unchained. Beserker can make can make 3 reactions per round.

Multiattack. Beserker can make 3 attacks.

• Greatsword. Melee weapon attack: +12 to hit, reach 5ft. One target. Hit: 13 (2d6 + 6) slashing damage.

"No One is Better than Beserker". When Beserker hits a creature with an opportunity attack, the creature’s speed becomes 0 for the rest of the turn.
Creatures provoke opportunity attacks from Beserker even if they take the Disengage action before leaving his reach reach.
When a creature within 5 feet of you makes an attack against a target other than Beserker then can use his reaction to make a melee weapon attack against the attacking creature.