Viper

To overcome the threat of almighty beings, hunters studied one of nature's deadliest predators ─ one capable of overcoming foes greater even than themselves: the viper. They are swift and agile, with dual blades like fangs to bite, or combine into a single weapon to weave about the battlefield. Named for the serpent that inspired their fighting style, the vipers of the Weald remain steadfast in their duty to defend the people.

Blade Stances

As a free action outside of combat, or at the cost of one blade die during, you may swap stances. Each stance will change your currently adopted fighting style as well as provide a bonus to subsequent attacks after the first hit. The stances are as follows:

Dual Blade Stance:
Fighting Style: Two Weapon Fighting (add modifier to damage of bonus action attack.
Stance Effect: You focus exclusively on your target. When hitting the same target with subsequent attacks, add your proficiency bonus to attack rolls.

Twinblade Stance:
Fighting Style: Great Weapon Fighting (reroll 1s and 2s)
Stance Effect: Your swings reach wide and carry your momentum into the blow. When hitting a different target with subsequent attacks, add your proficiency bonus to damage rolls.

When you choose this archetype at 3rd level, you learn techniques that are fueled by special dice called blade dice. Many techniques enhance an attack in some way. You can use only one technique per attack. You learn two additional techniques of your choice at 7th, 10th, and 15th level. Each time you learn new techniques , you can also replace one technique you know with a different one.

• Techniques:. You learn four techniques . Many techniques enhance an attack in some way. You can use only one technique per attack. You learn two additional techniques of your choice at 7th, 10th, and 15th level. Each time you learn new techniques , you can also replace one technique you know with a different one. Whenever you learn a technique (including the first time), you must choose an equal number of Dual Blades and Twinblade techniques .
• Blade Dice: You have four blade dice, which are d8s. A blade die is expended when you use it. You regain all of your expended blade dice when you finish a short or long rest. You gain another blade die at 7th level, 10th,  and one more at 15th level.
• Saving Throws. Some of your techniques require your target to make a saving throw to resist the technique's effects. The saving throw DC is calculated as follows:
• Maneuver save DC = 8 + proficiency bonus + Dexterity modifier

Techniques

The techniques are presented in alphabetical order.

[DB] Ambush

When you make a Dexterity (Stealth) check or an initiative roll, you can expend one blade die and add the die to the roll, provided you aren’t incapacitated.

[DB] Bait and Switch

When you’re within 5 feet of a creature on your turn, you can expend one blade die and switch places with that creature, provided you spend at least 5 feet of movement and the creature is willing and isn’t incapacitated. This movement doesn’t provoke opportunity attacks.

Roll the blade die. Until the start of your next turn, you or the other creature (your choice) gains a bonus to AC equal to the number rolled.

[DB] Disarming Attack

When you hit a creature with a weapon attack, you can expend one blade die to attempt to disarm the target, forcing it to drop one item of your choice that it’s holding. You add the blade  die to the attack’s damage roll, and the target must make a Strength saving throw. On a failed save, it drops the object you choose. The object lands at its feet.

[DB] Distracting Strike

When you hit a creature with a weapon attack, you can expend one blade die to distract the creature, giving your allies an opening. You add the blade die to the attack’s damage roll. The next attack roll against the target by an attacker other than you has advantage if the attack is made before the start of your next turn.

[DB] Feinting Attack

You can expend one blade die and use a bonus action on your turn to feint, choosing one creature within 5 feet of you as your target. You have advantage on your next attack roll against that creature this turn. If that attack hits, add the blade die to the attack’s damage roll.

[DB] Goading Attack

When you hit a creature with a weapon attack, you can expend one blade die to attempt to goad the target into attacking you. You add the blade die to the attack’s damage roll, and the target must make a Wisdom saving throw. On a failed save, the target has disadvantage on all attack rolls against targets other than you until the end of your next turn.

[DB] Grappling Strike

Immediately after you hit a creature with a melee attack on your turn, you can expend one blade die and then try to grapple the target as a bonus action (see the Player’s Handbook for rules on grappling). Add the blade die to your Strength (Athletics) check.

[DB] Lunging Attack

When you make a melee weapon attack on your turn, you can expend one blade die to increase your reach for that attack by 5 feet. If you hit, you add the blade die to the attack’s damage roll.

[DB] Precision Attack

When you make a weapon attack roll against a creature, you can expend one blade die to add it to the roll. You can use this maneuver before or after making the attack roll, but before any effects of the attack are applied.

[DB] Riposte

When a creature misses you with a melee attack, you can use your reaction and expend one blade die to make a melee weapon attack against the creature. If you hit, you add the blade die to the attack’s damage roll.

[DB] Tactical Assessment

When you make an Intelligence (Investigation), an Intelligence (History), or a Wisdom (Insight) check, you can expend one blade die and add the blade die to the ability check.

[DB] Trip Attack

When you hit a creature with a weapon attack, you can expend one blade die to attempt to knock the target down. You add the blade die to the attack’s damage roll, and if the target is Large or smaller, it must make a Strength saving throw. On a failed save, you knock the target prone.

[T] Brace

When a creature you can see moves into the reach you have with the melee weapon you’re wielding, you can use your reaction to expend one blade die and make one attack against the creature, using that weapon. If the attack hits, add the blade die to the weapon’s damage roll.

[T] Commander’s Strike

When you take the Attack action on your turn, you can forgo one of your attacks and use a bonus action to direct one of your companions to strike. When you do so, choose a friendly creature who can see or hear you and expend one blade die. That creature can immediately use its reaction to make one weapon attack, adding the blade die to the attack’s damage roll.

[T] Commanding Presence

When you make a Charisma (Intimidation), a Charisma (Performance), or a Charisma (Persuasion) check, you can expend one blade die and add the blade die to the ability check.

[T] Evasive Footwork

When you move, you can expend one blade die, rolling the die and adding the number rolled to your AC until you stop moving.

[T] Maneuvering Attack

When you hit a creature with a weapon attack, you can expend one blade die to maneuver one of your comrades into a more advantageous position. You add the blade die to the attack’s damage roll, and you choose a friendly creature who can see or hear you. That creature can use its reaction to move up to half its speed without provoking opportunity attacks from the target of your attack.

[T] Menacing Attack

When you hit a creature with a weapon attack, you can expend one blade die to attempt to frighten the target. You add the blade die to the attack’s damage roll, and the target must make a Wisdom saving throw. On a failed save, it is frightened of you until the end of your next turn.

[T] Parry

When another creature damages you with a melee attack, you can use your reaction and expend one blade die to reduce the damage by the number you roll on your blade die + your Dexterity modifier.

[T] Pushing Attack

When you hit a creature with a weapon attack, you can expend one blade die to attempt to drive the target back. You add the blade die to the attack’s damage roll, and if the target is Large or smaller, it must make a Strength saving throw. On a failed save, you push the target up to 15 feet away from you.

[T] Quick Toss

As a bonus action, you can expend one blade die and make a ranged attack with a weapon that has the thrown property. You can draw the weapon as part of making this attack. If you hit, add the blade die to the weapon’s damage roll.

[T] Rally

On your turn, you can use a bonus action and expend one blade die to bolster the resolve of one of your companions. When you do so, choose a friendly creature who can see or hear you. That creature gains temporary hit points equal to the blade die roll + your Charisma modifier.

[T] Sweeping Attack

When you hit a creature with a melee weapon attack, you can expend one blade die to attempt to damage another creature with the same attack. Choose another creature within 5 feet of the original target and within your reach. If the original attack roll would hit the second creature, it takes damage equal to the number you roll on your blade die. The damage is of the same type dealt by the original attack.

Know Your Enemy

Starting at 7th level, if you spend at least 1 minute observing or interacting with another creature outside combat, you can learn certain information about its capabilities compared to your own. The DM tells you if the creature is your equal, superior, or inferior in regard to two of the following characteristics of your choice:

• Strength score
• Dexterity score
• Constitution score
• Armor Class
• Current hit points
• Total class levels (if any)
• Fighter class levels (if any)

Additionally, you gain another blade die (total of 5).

Slither

At 10th level, your blade dice turn into d10s. Additionally, you gain another blade die (total of 6).

When you leave melee range with one or more creatures, roll a dexterity saving throw. The DC for this is 10 + the number of creatures in range. You may expend a blade die and add it to the saving throw. You may do this after seeing the role prior to determining the outcome. On a success, you successfully disengage from the creature(s). On a fail, you provoke attack(s) of opportunity.

Relentless

Starting at 15th level, when you roll initiative and have no blade dice remaining, you regain two blade dice.

Additionally, you gain another blade die (total of 7).

Mastered Blade Stances

At 18th level, your blade dice turn into d12s. You may switch freely between stances in combat without spending blade dice.