Hex Nail's power is decent all around for clashing as an EGO, being able to reach a maximum power of 24 (26 at uptie III and above). However, its specialty is being able to inflict a specific type of debuff against enemies. While Awakening and Corrosion inflict the same type of debuffs (Pierce and Envy Fragility), the amount of fragility inflicted by each differs. In this case, Awakening inflicts more Envy Fragility than Pierce.
This means that Pierce-focused Identities will enjoy the debuffs of Hex Nail. Kurokumo Ryoshu, R Corp Heathcliff, and Molar Boatworks Ishmael are just a few Identities that gain a massive damage increase when paired with Hex Nail.
Hex Nail can also inflict Nails and Curse, which are nice added bonuses, but not all that important to the main draw of this EGO. Same goes for the 50% damage bonus against enemies with Curse.
Corrosion is almost the same as Awakening, except Corrosion has a lower max power at 22 (24 at uptie III and above) and it inflicts more Envy Fragility than Pierce. This means Identities with strong Envy skills benefit greatly, such as W Don, W Ryoshu, R Corp Heathcliff, and Rosespanner Rodion, just to name a few.
Interestingly, R Corp Heathcliff benefits from both debuffs thanks to Quick Suppression, but it's highly likely that you'll be having him go faster than your other Identities to take advantage of the skill's coin bonus power anyways.
This passive makes Faust deal more damage if she has any negative status effect on her, increasing her damage by 10% per status effect up to a maximum of 50%. While a good bonus if Faust ever gets hit, ideally she won't be getting hit in the first place, as she risks being staggered whenever that happens.
As a result, this means that this passive is most likely not going to see much use, unless fighting enemies that can inflict status effects without dealing damage.
Hex Nail's primary goal is to be a debuffer to inflict either a ton of Envy Fragility or Pierce Fragility, depending on your team and build. This means that Hex Nail primarily plays a support role to the rest of your hard-hitting team, letting your W Don demolish the enemy with a fully charged Rip Space for instance.
What this means as well is that you're going to want to use a Faust Identity that's fast, so she can outspeed her allies and go first. This is because the debuffs she inflicts apply on the same turn that she uses Hex Nail, and having her go last means that none of her allies really get to benefit from the debuffs she can inflict.
On uptie III, Awakening and Corrosion can inflict Curse, a unique status effect that inflicts a random debuff on an enemy on either their attack or defense. The fact that the debuff is random means that this status effect should be treated as a bonus and should not be relied on.
On uptie IV, Awakening and Corrosion can inflict Nails, a status effect that N Corp Identities benefit from with their skills gaining bonus depending on the amount of Nails an enemy has, but again, this should be treated as a bonus to its main selling points. This uptie level also makes Hex Nail deal more damage if an enemy has Curse, but as Hex Nail is better off for supporting your other allies, it's best to not abuse it too much, unless you're swimming in Envy resources, as the cost can rack up pretty fast.
Hex Nail is also one of the rare few EGOs in the game who only spends one type of EGO resource. In this case, it's Envy. This can be a double-edged sword, as while you won't have to worry as much in generating other resources to utilize Hex Nail, it is still an expensive EGO to use, requiring a minimum of 6 Envy resoruces to even get online. You may have difficulty getting passives that require a certain amount of owned Envy resources for instance to activate, for instance, or even have difficulties in using other EGOs that may want Envy resources.
Potential difficulties of resource management aside, Hex Nail can be an amazing tool for teams in helping you burst down an enemy from 1000 HP to 0, especially if they are staggered. Faust just needs to outspeed your DPS members that have either high damaging Envy or Pierce skills to let them reach their fullest potential.