When I did my combat arts (which I'll link the list of abilities, but the mechanics are in the other thread) I started lower impact and then went up
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homebrewery.naturalcrit.com
I had eleven 1st level Arts including the ability to make extra attacks if you hit, pushing an enemy 10 ft, disarming an enemy (which does not work on shields), giving an enemy disadvantage on a single attack, lunging forward an extra 5ft, reducing an enemies speed, granting advantage on an allies attack, knocking them prone, using a chain/whip to grapple and a marking mechanic.
Most of these arts increased in strength at level 5 or 9. Disarm allowed you to catch the item you knocked out of their hands, disadvantage increased to every attack made by the enemy on their next turn, the lunge becomes 5ft extra reach and 10ft of extra movement, the advantage on an attack becomes disadvantage on a save, the push got a lot further (5 x mod)
The most powerful increase happened to the prone, at level 13 it also imposes the dazed condition, which is brutal.
5th level arts also had eleven total. These include blinding a nearby opponent, reducing falling damage as a reaction, using your reaction to intercept an attack made against an ally, attacking an enemy that enters your reach, goading an enemy into attacking you (this can force them to move, but they don't trigger AoO's if they do, for balance), imposing the dazed condition, attacking someone who missed you, increasing AC against AoO's, allowing an ally to disengage and move half speed, reduce damage you take from a hit, and imposing the frightened condition.
Most of these arts improved at levels 9 or 13. More damage reduction from falling, increasing the range of the switch with an ally, allowing an ally to disengage and use their full speed, blinding every chosen enemy adjacent to you, then there are a few notable ones.
The fear effect at level 9 allows you to target anyone within 30 ft, instead of the person you hit. Then at level 13 you can choose to frighten someone and everyone adjacent to them.
The goad and the Daze both end up lasting for repeated rounds, fading with a successful save.
And probably the most powerful, at level 17 the attacking an enemy that enters your range no longer takes a reaction if you successfully pull it off.
Level 9 only had four new abilities. A crippling attack that reduces the targets speed by half, and gives disadvantage to dex saves, the ability to break weapons and shields (but not armor), the ability to give yourself and your allies +2 AC, and the ability to turn any attack you make into a minor AOE hitting adjacent targets of your choice.
Level 13 got six new abilities, and this is where I started going more supernatural. The ability to use a chain and restrain any number of targets within a 20ft cube, the ability to drop an enemy to zero hp if your attack roll exceeds their current hp, an attack that hits the ground instead of a target, knocking everyone within 10 ft prone and creating difficult terrain. The ability to volley arrows into a small AOE, a teleport slash that moves them 20 ft an attacks anyone within 5ft of the line they moved along as an attack, and then a reaction which allows you to either reduce the attack roll of ANY ranged attack, or increase the save versus a line spell. If you force the attack to miss, or succeed on the save, you redirect the attack or spell effect to another creature within range. The creature gets advantage on the saving throw if it was a line.
And for level 17 arts.... I ran out of ideas
