Marco ate a Devil Fruit referred to as a Mythical Zoan type; an immensely powerful type of Zoan Devil Fruit, said to be the rarest type, even rarer than Logia fruits. His Devil Fruit enables him to transform into a phoenix. It is because of this ability that he is identified as “Marco the Phoenix”. While this fruit’s power is classified as a Zoan, due to the uniqueness of the phoenix, the additional powers it grants may be considered similar to those of Paramecia (the somewhat “superhuman” power that affects the user’s body: regeneration) and Logia (the generation of blue phoenix flames).
This Devil Fruit gives Marco increased physical attributes (as is with all Zoan types) and the rare ability of flight, as well as the possibility of launching aerial attacks. During the Battle of Marineford, Marco showcased his aerial maneuverability by traversing quickly across the battlefield and supervised the assault in Whitebeard’s place. He can transform his feet into phoenix talons, with which he can slash his enemies.
Like other Zoan users, Marco is able to take a hybrid human-beast form. However, Marco’s control over his transformations seems to be the greatest of any other Zoan user shown so far, as unlike most other Zoan users (Laffitte, Chopper, and Onigumo, possibly being the only known exceptions), Marco can transform selective parts of his body into phoenix form without changing his whole appearance. In his most commonly seen human-beast form, Marco only transforms his arms into wings of fire (sometimes choosing to maintain his hands) so that he can fly and still attack with standard kicks.
The fruit’s greatest attribute, however, is that by transforming into a phoenix of blue flames at will, Marco can regenerate any wounds with the blue fire he generates, much like how a phoenix is said to rise from its own ashes. Because of this, Marco is very resilient and can take a huge amount of damage in his phoenix form with no visible consequence other than the time taken to regenerate. He was thus able to block a barrage of simultaneous lasers from Kizaru, and even intercepted, with the help of Busoshoku Haki, Akainu’s magma punch, an attack that was so damaging it burned and eventually took the life of the fire Logia-user Ace; the latter feat suggests that phoenix flames are superior to Akainu’s magma and Ace’s fire, or this could have just been due to Marco’s healing powers. These blue flames are not hot and they do not burn or spread like normal fire; instead, they are what allow him to heal, though there is a limit to the regeneration and are referred to as the “Blue Flames of Resurrection” Marco can recover from any damage he accumulates in his human form by reverting to his phoenix, or hybrid phoenix form, or just by summoning blue flames around his body. He has even been seen recovering using mere scattered flames and turning into his human form simultaneously, proving that he is quite resilient and calm when prepared for an impact. This allows him to even recover from any injuries taken while touching seastone, but only after he stops being in contact with it. This gives Marco a huge advantage that no Logia user has, since the damage done to Logia users with their powers disabled remain permanent. This is not the case with Marco, as he can heal when necessary.
Despite the fact that it cannot be used as a weapon, he can still summon the blue flames around his person, in his human form (possibly by partially shifting into his hybrid form or full-phoenix form), as seen when he engulfed his arm with the said flames as he prepared to confront Akainu.
Other than the aforementioned weaknesses, Marco is also susceptible to the standard Devil Fruit weaknesses like any user.