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1. Go seriously min-max on this: Con>Str>Dex>Wis>Cha>Int.

2. Since Half Orc is the best racial choice for Barbarian, followed by Goliath and variant Human, pick one of those three. The variat Human allows you that feat at level 1.

In almost any situation, this Barbarian can "help" rather than attack and provide other melee attackers with advantage on their. While so doing, the initial rage may expire if you have not taken damage, but the other party members should have been able to build some momentum for that encounter.

You want to benefit from unarmored defense, and get more HP, and make your Con saves. (See below)

Possible 1 level of MC in Rogue

Get athletics Expertise. Get another skill. Your grappling just got better. Your shoves got better. You knocked prone got better. If you knock an enemy prone, and your paladin ally attacks twice with advantage, Divine Smites can get pretty nice nova damage, particularly on a critical hit.

1. Reckless attack helps with that, above and beyond support.
2. Extra Attack helps with that;
3. Brutal Critical helps with that;
4. Relentless Rage helps in keeping you up, keeping that rage bonus damage going, and supporting round after round, until you miss that Constitution save (See above for why ASI in Constitution is a good thing)
5. Persistent Rage aids in the entire Ancestral Guardian approach, since rage fires those abilities.
6. Indomitable Might: better grappling, better shoving, better Help actions ...
7. Primal Champion (If you don't choose that one level MC in Rogue): Strength and Constitution go up by 4. All of what you are doing above are improved.

1. Go seriously min-max on this: Con>Str>Dex>Wis>Cha>Int.

2. Since Half Orc is the best racial choice for Barbarian, followed by Goliath and variant Human, pick one of those three. The variant Human allows you that feat at level 1.

In almost any situation, this Barbarian can "help" rather than attack and provide other melee attackers with advantage on their attacks. While so doing, the initial rage may expire if you have not taken damage, but the other party members should have been able to build some momentum for that encounter.

You want to benefit from Unarmored Defense, and get more HP, and make your Con saves. (See below)

Possible 1 level of multi-class in Rogue

Get athletics Expertise. Get another skill. Your grappling just got better. Your shoves got better. Your knocking prone got better. If you knock an enemy prone, and your paladin ally attacks twice with advantage, Divine Smites can get pretty nice nova damage, particularly on a critical hit.

1. Reckless attack helps with that, above and beyond support.
2. Extra Attack helps with that;
3. Brutal Critical helps with that;
4. Relentless Rage helps in keeping you up, keeping that rage bonus damage going, and supporting round after round, until you miss that Constitution save (See above for why ASI in Constitution is a good thing)
5. Persistent Rage aids in the entire Ancestral Guardian approach, since rage fires those abilities.
6. Indomitable Might: better grappling, better shoving, better Help actions ...
7. Primal Champion (If you don't choose that one level multi-class in Rogue): Strength and Constitution go up by 4. All of what you are doing above is improved.

• @mattdm suggests (if the build is going to 20) consider fitting in three levels of Rogue and take the archetype Mastermind: this provides Help as a bonus action and at range. This will depend on your party's composition, but might be a good it.

There is a decent Barbarian build that focuses on support in XGtE

Yes: a non-magic Barbarian that focuses on support is in XGtE