WARNING: The following contains spoilers for Season 5 of The Seven Deadly Sins, now streaming on Netflix, as well as the end of the manga.
The Seven Deadly Sins is full of people with extraordinary powers, but they are unique to each person based on their race and training. Much of Meliodas' powers are from his demon lineage, Elizabeth's from her angel lineage, etc. Even humans can gain powers others only dream of. Ban is one of those humans, having immortality thanks to the Fountain of Youth and increased physical abilities thanks to his time in Purgatory. He even took on the Demon King when he possessed Meliodas' body, receiving very few injuries in the process. So here are a few facts about how Ban is able to perform all these amazing feats.
Ban Can Steal Your Organs
One of Ban's special abilities in The Seven Deadly Sins is called Snatch, which allows him to steal physical objects or even powers from other people. There is a limit to its reach though, as the abilities can only be physical -- like stamina or speed -- and cannot be used to cause harm to another being. This doesn't stop Ban from causing damage, as he's shown to use his Snatch powers to steal the organs from another person's body.
So while Snatch can't slice an opponent in half, it can rip out their still-beating heart. Counter to this, it seems to allow Ban to give his physical attributes to others using the "Gift" technique. He can also turn invisible, possibly by stealing others' perception of him. This lack of perception also seems to include objects through which one can watch others, like a crystal ball.
Ban Is Immortal
Thanks to the Fountain of Youth, Ban is -- or rather was -- immortal. He went to the Fairy King's Forest in search of the Fountain, but instead found its guardian Elaine. The two formed a relationship, which played a major part in Ban gaining his immortality. Elaine couldn't leave the forest because her brother, the Fairy King, was not there to do his duties, including keeping the Fountain safe.
When a demon began burning down the forest, Ban and Elaine were both gravely injured, so she granted Ban the immortality by forcing him to drink water from the fountain. Later in The Seven Deadly Sins, in his quest to revive Elaine after her death, he gave up the immortality he desperately sought in order to bring her back to life.
Ban Can Wipe Out an Army in One Swing
Using his Sacred Weapon Courechouse, Ban's powers increase dramatically. With an ability called Super Concentration, his physical and mental acuity reach their absolute limits. Not only this, but Courechouse can extend the chains that hold its segments together and bend to any angle. This is best shown when he takes out an army of Indura offspring with one large swing of the staff. This particular power comes from the weapon itself rather than Ban, but Courechouse seems to have been crafted especially for him, so it's unknown if others would achieve the same feats if they used it.
Ban Has a Healing Factor
Thanks to drinking the water from the Fountain of Youth, not only is Ban immortal, but he also has a healing factor. Any wound he sustains in The Seven Deadly Sins is healed almost instantly, no matter how grievous it seems. Not only this, but his own blood has also taken on a healing quality.
It's used several times to heal the injuries of others and even restored the Fairy King's Forest after it was burned down by the demon that killed Elaine. Unfortunately, Ban lost immortality when he gave up his immortality to bring Elaine back to life, meaning he also lost the ability to heal others.
Ban Is a Master Thief
Growing up in Ravens, Ban was beaten and abused by his parents. As a result of his horrid home life, he resorted to stealing in order to survive. He eventually ended up in Aberdeen Prison, where he met Zhivago. The two would escape, however, and Zhivago teaches Ban how to steal, though he does get caught for a while. He continues training even after they part ways, becoming known as Bandit Ban and, eventually, the Fox's Sin of Greed.
At one point Ban even stole all the stuffed animals in the kingdom, causing all of its children to cry. His love of stealing is what leads him to meet Elaine and gain the powers of the Fountain of Youth. Eventually, he gives up his thieving ways for good and become King of Benwick, with his beloved Elaine as his queen.