Frenzied Knight

With skills learnt from untraditional training, fey heritage or genuine madness, Frenzied Knights are an archetype of the Fighter who adapt to the environment to use it to their advantages and use their frenzied state influenced by nature to overcome obstacles unachievable by anyone else. There is a subtle magic in everything they do, enhanced by the nature around them. As their strength and power increases, their presence in the natural world and its order becomes more clear. It is not uncommon for Archfey to train their soldiers in this way, and the origins of this archetype have strong roots in the Feywild.

Natures Frenzy

When you choose this subclass at 3rd level, your fighting spirit emerges whilst in the natural world. On your turn as a bonus action you can enter a frenzy. Whilst in a this frenzy you have advantage on Strength checks and checks against being charmed or put to sleep. You can also add your proficiency bonus to your damage rolls. Your frenzy lasts for a minute and ends early if you are knocked unconscious or you end it as a bonus action. You can frenzy an amount of times equal to your proficiency bonus.

Enviromental Attack

At 7th level you have learnt how to use the environment and terrain resources around you to aid your attacks. As a bonus action you can use an Environmental Attack from the list below as an Improvised Attack. The required resource must be within 5 feet of you or must have been gathered previously.

Environmental Attack Options: 
 Mud:  Range 20/60, deals 1d6 cold damage + your Strength modifier.
Sand: Range 20/60, deals 1d4 piercing damage and the target is blinded until their next turn. 
Rocks: Deals 1d8 bludgeoning damage + your Strength modifier.
Thorns: Covers a 5ft area, any creature within that area must succeed on a DC 10 Dexterity saving throw or take 1d6 piercing damage   
Stick: Deals 1d6 slashing damage + Strength modifier, or, if the target has an Intelligence score of 5 or lower, you can throw it 10 feet instead of deal damage. The target then becomes Charmed by you for as long as you keep using your bonus action to throw the stick for it.

Precious Weapon

At 10th level you select a weapon which becomes your most prized possession, called your Precious Weapon. Your Precious Weapon gains these effects: 

Improved Critical: When using this weapon you land a critical hit on a 19 or 20 
Boon of Nature: Attacks from your Precious Weapon count as magical and you can use it as a spellcasting focus for any spells you cast.
Linked by Wildness:  During your frenzy this weapon cannot be removed from your person against your will and you can use your Environmental Attack feature twice. 

Natural Magic

At 15th level,  nature has bonded with you and you have gained some of its magic. You gain 3 cantrips, two 1st level spells and one 2nd level spell from the Druid spell list which you can cast each once per long rest.

Frenzied Surge

At 18th level you can release the pent up energy of nature stored inside of you. As an action the ground within 30ft of you becomes difficult terrain as otherworldly flora grows rampantly from the ground. Every creature within 30ft must succeed on a DC 15 Dexterity saving throw or take 10d6 force damage and be grappled by vines on a failed save or take half as much and not be grappled on a successful save. You then fall prone and gain 1 level of exhaustion.