The moment you think about a mutant you immediately start thinking about their powers and usually all mutants have well-defined powers. But that is not the case with Apocalypse. His powers are undefined. But as far as we know he has the ability to change his body at his will by controlling his body’s molecules. This enables him to heal almost in an instant and to transform his body into many deadly weapons. He is also believed to be immortal! He can increase his physical strength to a point where he surpasses Hulk!
It is not a co-incidence that Apocalypse has just 4 sidekicks in the movie. It is believed that he always appoints 4 people as his personal guards also called as his ‘Horsemen.’ He also has the power to enhance the mutant abilities of his horsemen. His most notable Horseman is Angel who later on becomes Archangel. Wolverine has also served as his horseman for a brief period of time. But in the movie, they only show Angel, Storm, Magneto and Psylocke as his Horsemen.