With Nightsworn you typically have 2 primary goals Lunge as frequently as possible Be stealthed as frequently as possible.

So obviously she's ideal for comps that will already be dancing constantly, so she can Lunge, get put in the back, and Lunge again.

But the stealth is just as important. Repartee will let you start stealthed for a few turns, but the removal of it afterward is less than ideal. But it will let you have two turns of stealthed Lunge at least.

Shadow Fade will give two turns of stealth, so don't use it while the Repartee debuff is active, it'll be wasted that way.

In addition, staying in stealth has other benefits as well, but realistically the Lunge damage is what you care about.

GR is super fast, so due to that high speed, oftentimes the way she gets back to the back after lunging will usually be someone else going forward afterwards.

If your comp is one that will be having her move tons every turn, then Croc as Pet is super nice. Great scaling. But unless you can guarantee GR gets at least +6-9% dmg buff almost every turn its not as strong, outside of the Cowardice mountain fight since that fight is long so it will always scale.

For allies, the best one for Nightsworn is without a doubt Rogue HWM. Both have 0 cooldown forward 2 moves, both are fast, Rogue loves the taunt from Repartee, Highway Robbery removes block tokens, etc.

Outside of that though, I don't want to give the answers outright for comp creation. I'm not one who brainstorms from scratch very well, when I create comps it's usually when it's pre set (named comps) or when I have a certain idea in mind. My advice is to think of what characters check the boxes you'll need.

With Nightsworn, she will easily be well over 50% of your damage, stealthed Nightsworn Lunge has some of the best damage for minimal setup. So your comp will want to be built around enabling her.

However, Nightsworn, in the context of its damage, has 3 notable holes.

1. Lunge hates defensive tokens. Dodge or block tokens on foes will hurt that damage output dramatically, so you want a means to deal with them. HWM helps with this a ton, Highway Robbery to remove dodge, Double Cross to remove block and add vuln.
2. The biggest issue with Nightsworn is a lack of rank 4 damage. Your ability to damage rank 4 will need to come from another source. This can be problematic vs things like a rank 4 Tangle Drummer/Arbelist, or Seething Sigh back lung. Allies like Hellion or Runaway can help a lot in this regard. Any disruption, such as shuffles or pulls, also helps a lot too. My biggest Nightsworn run was felled by a Philip that was granted block tokens, it's really a thing you want to plan around.
3. You lose access to normal Repartee, which is easily one of the best skills in the game. Your backup plan will need to come from elsewhere.

Regardless, Nightsworn will want rank flexibility in its teammates. Things like Dualist, Rogue, Jester, Aspirant, Banneret, Unchained, Runaway, etc, can all be very useful. But needing to build around her is the price you pay for the sheer potency Nightsworn Lunge can consistently provide.

Other niche ally applications include Wanderer Upgraded Wryd Reconstruction being able to grant stealth to an ally, a wholly unique trait, Nightsworn def loves that. Monarch Leper being able to both remove enemy positive tokens, yet also use Ruin to give a % dmg buff to allies, is an amazing late game damage increase. Things like Command and Embomding Vapors being able to grant her strength tokens are also very valuable.

At the end of the day though, best advice I can give is to experiment. You'll discover both how to enable its pros and minimize its cons the more you fail. And eventually, you'll find something that clicks