Haki

Her specialty is her observation haki which she uses pretty much 24/7. It is a crucial part of her abilities as a former Ciper Poll agent, using it for infiltration and spying, avoiding detection and securing information. Empowered by her snake devil fruit, she's able to sense people, certain things, and track from far away by flicking her tongue, much like how a snake smells and detects presences around them. She's also able to pick up on peoples intentions and feelings if they are within 15 meters of her.

Armament Haki

She also is able to use Armament Haki, something she mainly uses for her double finger pistol attacks and other offensive means. Other than that, she doesn't use it much unless she physically can't dodge and incoming attack, something she tries to avoid at all costs, focusing on dodging and evasion.

The Six Powers (Rokushiki)

Having trained from a young age as a Cipher Poll agent, Mello has decent mastery over most of the skills, albeit like most others she has her specializations which she exceeds at.

She has high mastery over Shigan (finger pistol), Kami-e (paper art), Tekkai (iron body), while her specialization being Shigan and Kami-e. The rest like Geppo(moonwalk) and Soru(shave) she's completely average at.

Grip Strength

Part of the reason why she prefers to use a modified finger pistol move by using two fingers instead of one is because it is easier for her to grab a hold on someone that way. Having adapted a small trait from other snake species, her grip strength is highly destructive and unrelenting. Able to hold on to even small grips while being thrown around, she's very hard to get off once she's got a hold of you.

Gloves and protection

Her half gloves act as extra protection for her fingers that are covered, with a special texture letting her get a better grip on things as well. But since only her pinky and ring finger is covered, those are the only two fingers benefitting by it, as her other fingers are used for her special venom coated finger gun attacks.