Diavolo/Abilities and Powers

Stand
Diavolo's Stand is King Crimson, an extremely powerful Stand with tremendous physical strength and the ability to erase time up to a 10 seconds time frame as well as predict anything that happens over the following 10 seconds. Although it has some limitations, King Crimson renders him essentially invincible in a fight as he can either foresee and counter the enemy's actions or render them meaningless by erasing the timeframe in which they happen.

Double Personality
Despite (likely) being human, Diavolo and Doppio share many minor abilities in changing their physical appearance. Doppio looks to be around 17 years of age and shorter than Bucciarati. However, while attacking that same man as Diavolo, he appeared to be a head taller, if not more, as well as being muscular. Furthermore, when Diavolo takes over, Doppio's freckles disappear and his voice deepens, and it may be possible that his hair can become longer or shorter than Doppio's. According to Diavolo, it takes him roughly 10 seconds to completely take over Doppio's body, but the transformation back to Doppio is instant.

While Doppio is in control, Diavolo has quite a few abilities, border-lining omniscience. He was able to tell that the taxi driver didn't see the picture of Donatella that Doppio was carrying, despite his subordinate's beliefs, and was later able to see the lurking Risotto. Diavolo also seems to be able to manipulate Doppio's memories, as Diavolo remembers everything and can see everything that happens to Doppio but not vice versa, although it's unknown how much of this is based off Doppio's possible poor memory. Diavolo can communicate with Doppio through any kind of object while not in control, granting his subordinate the belief that his alter ego is another person all together. Although we haven't heard the quality of these "calls" yet and whether or not the objects alter the quality of Diavolo's voice, Doppio can always hear his alter ego's voice through the object. Doppio also, on occasion, forgets that he's been able to communicate with Diavolo, but he consistently has never realized he's been using a broken or non-phone object. These "phones" have ranged from ice cream to frogs, to cigarettes to toys, and of course Doppio always carries on him a broken or dismantled phone headset.

Soul Manipulation
Diavolo is for unknown reasons, exceptionally knowledgeable about souls and their mechanisms, and is also equally skilled at manipulating his own soul.

Diavolo shows uncommon knowledge about souls, for instance being able to tell the near dying Bucciarati's state and then correctly guess that he can only see souls. Knowing that souls of family members have the same "scent", Diavolo is able to grant a shard of his soul to Doppio to disguise himself as Trish's soul. Moreover, under Chariot Requiem's influence, Diavolo has been able to control in which body he could go, although he otherwise couldn't freely control it.

Although Diavolo could exert subtle control of his own soul, he remains subject to the powers of soul-manipulating Stands such as Chariot Requiem.

Spiritual Connection
As Trish Una's father, Diavolo has a spiritual connection to her. By instinct, he can sense that she is indeed his daughter and was able to feel that she was alive despite being informed that the plane she was on had crashed.

Intelligence
Diavolo is a gifted tactician and is generally more intelligent than average.

As the proofs of Diavolo's abilities, the Boss has built a powerful gang with influence spreading across Italy in a matter of years. To avoid his enemies spying on him, Diavolo has proved to be imaginative in delivering his orders, using proxies, computers, dead drops, or even exploiting his subordinates' Stand abilities so only they could access the messages.

During a fight, Diavolo usually relies on his King Crimson's power and favors straightforward tactics like erasing time and positioning himself for a fatal strike. However, Diavolo has also shown to be rather observant, taking note of any event and keeping tabs on his enemies' abilities. He notably predicted that Giorno Giovanna's wit would become a real nuisance to his plans and treaded carefully with him. Diavolo also kept observing the apparently defeated Team Bucciarati from afar and managed to correctly analyze their state of mind and subsequently roughly guess their goals. Finally, Diavolo was the first and only one person to be observant enough to see the mechanisms of Chariot Requiem and guess its weak points, enabling him to disable the Stand effortlessly.

Diavolo has shown to be able of thinking on his feet, not panicking when he was chased by Bruno Bucciarati and Narancia Ghirga in a body deprived of hemoglobin and quickly using the surrounding fauna to replenish his blood. He also subsequently exploited this opportunity to assassinate Leone Abbacchio. Likewise in Rome, an accidental meeting with Bruno was exploited by him to approach Polnareff and assassinate him. Diavolo's arguably most effective tactic was during his confrontation against Risotto Nero, during which he exploited both the presence of Team Bucciarati, Risotto's own scalpels, and his own weakened state to manipulate Aerosmith into shooting only Risotto and turn the tables against the assassin.