The following is an alternative / full replacement of the Wild Heart subclass for use in my campaigns.
Barbarians who follow the Path of the Wild Heart view themselves as kin to the predatory animals of the natural world. They learn magical means to connect and communicate with Beasts, and their Rage heightens their connection to primal power as it fills them with supernatural might.
Your Rage taps into primal power, lending you feral adaptations. Whenever you activate your Rage, you gain one of the following options of your choice for the duration of the Rage. In addition, at the start of your turn while your Rage is active you may end your current Rage and enter a new Rage (no action required) to choose a different Feral Rage feature option.
*Aquatic. You tap into the power of deadly aquatic animals such as sharks or barracuda. You grow gills and can breathe underwater, you have a Swim Speed equal to your Speed, and you gain Darkvision with a range of 30 feet or improve your existing Darkvision by 30 feet. In addition, if you fall or jump from any height and land in a body of water that is large enough to hold you and is at least 5 feet deep, you take no damage and are unharmed.
*Arboreal. You tap into the power of fierce tree dwelling animals such as various primates and some great cats. You have a Climb Speed equal to your Speed, and once per turn you can jump up to 10 feet without provoking Opportunity Attacks by spending 5 feet of movement. You may use this jump option even if you are Prone, removing the Prone condition, and you have Advantage on any ability checks you must make as part of this jump.
*Avian. You tap into the power of majestic raptors such as falcons or eagles. You grow feathered wings and have a Fly Speed equal to your Speed but cannot fly while wearing armor or if encumbered. In addition, you can see twice as far and have Advantage on sight based Wisdom (Perception) checks.
*Terrestrial. You tap into the power of swift pursuers such as cheetahs or wolves, or overbearing chargers such as bulls, rhinos, rams, or boar. Your Speed improves by 10 feet, you can take the Dash action as a Bonus Action during your turn, and Opportunity Attacks targeting you have Disadvantage.
You gain Expertise with Nature if you are already proficient, otherwise you gain Proficiency with Nature. You also learn your choice of Druidic or Sylvan.
In addition, you may expend a use of your Rage and choose Aquatic, Arboreal, Avian, or Terrestrial to force a Beast of that kind that you can see within 60 feet to make a Wisdom saving throw (DC 8 plus your Wisdom modifier and Proficiency Bonus). On a failure, the Beast has the Charmed condition until you finish your next Short or Long Rest. The Beast has Advantage on the save if you or your allies are fighting it. If you or your allies deal damage to the target or harm other Beasts of its kind, the effect ends immediately.
You have a telepathic link with the Charmed Beast while the two of you are on the same plane of existence, through which you can communicate basic ideas and feelings, and use any of the Influence action's skill options on the Beast. The Charmed Beast is Friendly to you and your allies but will not endanger its own best interests, means of survival, or life.
Most Beasts have little to say about topics that don't pertain to survival or companionship, but they can give you information about nearby locations and monsters and can scout and act as a lookout or distraction for you.
When you finish a rest, for each Beast currently Charmed by you in this way, you may choose to immediately expend a use of your Rage to prevent the condition from ending until you finish your next Short or Long Rest.
Your Feral Rage improves. While your Rage is active, once per turn if you move at least 10 feet toward a target immediately before hitting it with a melee weapon or Unarmed Strike you can choose to gain 1d12 bonus damage of the same type as the attack. The type of movement you need to use is determined by the option you chose when you activated your Rage.
*Aquatic. You must swim at least 10 feet to use this feature.
*Arboreal. You must jump at least 10 feet to use this feature.
*Avian. You must fly at least 10 feet to use this feature.
*Terrestrial. You must run at least 10 feet to use this feature.
A Beast Charmed by your Wildergift feature is now willing to endanger themselves to help you, including fighting on your behalf. In combat they act during your turn and will move and use their Reaction on their own, but the only action they will take is the Dodge action unless you use your Bonus Action to command them to take an action in their stat block or some other action.
If you have the Incapacitated condition they will act on their own, but will attempt to drag you to safety or otherwise protect you if possible. They will not fight to the death if they can avoid it, and will flee dangerous situations if they have 4 or fewer Hit Points.
Your Rage suffuses you with incredible primal power. While your Rage is active you gain the following additional benefits:
*Aquatic. When you strike a target with Staggering Blow you gain the benefits of the Disengage action.
*Arboreal. When you strike a target with Hamstring Blow you score a Critical Hit on a roll of 19 or 20 on the d20.
*Avian. When you strike a target with Sundering Blow, until the end of the turn that target cannot make Opportunity Attacks against you and your Fly Speed improves by 10 feet.
*Terrestrial. After you push your target back with Forceful Blow you may also choose to knock them Prone.
The DM might allow a player of this subclass to choose the following variation. It allows a player to give up tactical flexibility for greater thematic focus and consistency.
When you take this subclass at 3rd level, you may choose to gain the Feral Affinity feature instead of the Feral Rage feature.
When you take this subclass, instead of gaining the Feral Rage feature you may instead choose one of the options of Feral Rage (Aquatic, Arboreal, Avian, or Terrestrial). You lose the flexibility of choice when raging, but gain the benefits of the selected option all the time whether you are raging or not.
For instance, if you choose Avian as your Feral Affinity you gain the benefits described for the Avian option of Feral Rage all the time, and thus have wings and a Fly speed.
Furthermore, when using Wildergift to Charm a Beast you must choose the same option you chose for Feral Affinity. For instance, if you chose Avian for Feral Affinity then you can only use Wildergift to Charm avian Beasts. However, the saving throw DC to resist the feature is increased by 2 and the range is improved to 120 feet.
If you would later gain Improved Feral Rage you instead gain Improved Feral Affinity for the same chosen option. You enjoy the benefits of the corresponding Improved Feral Rage option all the time. For instance, if you choose Avian for Feral Affinity at 3rd level, then you gain the Avian option for Improved Feral Affinity when you reach Barbarian level 6.
Finally, if you would later gain Superior Feral Rage you instead gain Superior Feral Affinity for the same chosen option. You enjoy the benefits of the corresponding Superior Feral Rage option all the time. For instance, if you choose Avian for Feral Affinity at 3rd level, then you gain the Avian option for Superior Feral Affinity when you reach Barbarian level 14.