Path of the Battle-trance

Not all barbarians harness anger or fury to dominate the battlefield. If instead your warrior seeks out monks for their training, they may learn to access a meditative battle-trance, imbuing them with both the power of a violent rage and the calm control of the wisest monk. A barbarian in a battle-trance is less of an unstoppable force and more of an immovable object.

Trance

Starting when you choose this path at 3rd level, your 'Rage' is replaced by 'Trance', though you still gain all the benefits of rage. Until the Trance ends, any attacks or actions used to shove you or knock you prone are rolled with disadvantage, and on a failure the attacking creature incurs an opportunity attack from you if they are within range. While in Trance, you gain advantage on Wisdom saving throws.

In your battle-trance, you can hear and understand anything that is said in any language you understand, but cannot speak save for the use of any hand-signs you may know.

Stillness of Self

Beginning at level 6, you develop a deep understanding of your instincts and emotions. While in your Battle-trance, you are immune to being charmed, frightened, or stunned. In addition, you are resistant to psychic damage, and any attempt to cast detect thoughts on you will render only a blank mind. If your Trance ends while a detect thoughts spell is still active, your thoughts become visible and you become vulnerable (disadvantage) to any attempts to probe deeper.

Relentless Song

Once per long rest, you may use an action to begin a wordless, rhythmic dirge or song. While the song is active, pick one:

1. You and up to 6 allies within 15 feet temporarily gain the 'Alert' feat: you cannot be surprised, you have a +5 bonus to initiative, and creatures unseen by you do not gain advantage on their attack rolls against you.

or

2. You and up to 6 allies within 15 feet gain temporary hit points equal to your barbarian level. If an ally affected by your song drops to 0 hit points and is not killed outright, they may choose to immediately expend 1 hit dice and heal that amount. An ally may only make use of this effect once per song.

or

3. If you or any ally within 15 feet are under the charmed condition, you may begin your song to end the effect. If you are not interrupted, the charmed condition ends at the end of your next turn. Any allies who are charmed and freed by your song cannot be charmed again for 24 hours.

This song lasts for 10 minutes and is concentration. Any creature affected by your song cannot be affected by a song again until they have completed a long rest.

Powerful Stance

Beginning at level 14, once per long rest you can take an action to plant your feet and adopt a powerful stance, provided you are not restrained or prone. While in this stance, your effective size increases by one metric (for example, medium to large) and your speed becomes 0. While in this stance, you cannot be knocked prone. You gain a +10 bonus to strength checks and saving throws and do an additional 2d6 damage on any armed melee attacks (additional 1d6 to unarmed strikes). One allied creature you designate can share a space with you provided they are one size smaller than your current size.

You are able to hold this stance for up to 10 minutes, or you can drop it as a bonus action. If you are forced out of the stance due to incapacitation or unconsciousness, or if the ground you stand on is removed from underneath you, you gain a level of exhaustion.