Destroyer Feat

You bring ruin to the battlefield, cleaving through hordes. You gain the following benefits:

Prerequisite: 4th level

• Ability Score Increase. Increase your Strength or Constitution by 1, to a maximum of 20.
• Cleaving Blows. When you reduce a creature to 0 hit points with an attack, you can apply any overflw damage (damage dealt by the attack over what was required to bring the target to zero) to another creature within 5 feet of the target, if the attack roll would also hit that target.
• Gain the Whirlwind Slash special attack (below).

Whirlwind Slash - Active Ability (Attack)

• When you take the Attack action on your turn, you can replace one of your attacks with spinning your weapon in a massive arc with great force. All creatures of your choice within 5 feet of you must make a Dexterity saving throw. On failure, they take 2d6 + your Strength modifier damage, or half as much on a successful save. The number of d6 increases by one when your proficieny bonus increases (with the total number of d6 equaling your proficieny bonus).

Once you use this feature, you cannot use it again until you complete a short or long rest.
Source: KCLL, page 182

Active Martial Feat Save DC:

• Any time an active martial feat requires a saving throw, the DC is 8 + your Strength or Dexterity modifier (your choice) + your proficiency bonus.