He has a high pain tolerance - Abyss has been slammed into thumbtacks, barbed wire, tables, you name it. The amount of pain Abyss has endured is unbelievable. This makes him a formidable often dangerous opponent in and out of the ring.
Abyss has great ring psychology and story-telling - Unlike hardcore legends like Mick Foley, Abyss used ring psychology well enough to avoid many injuries. He is very smart and knows how the rules work. He knows how to use momentum to his advantage or to sell his or his opponents moves.
Abyss skillfully uses size and strength - Abyss isn't just a big buff guy with no intellect. He's mobile, strong, clever, strategic, and destructive. He has many impressive moves including the black hole slam.
Overall, Abyss is one of the most underrated hardcore wrestlers who ought to have more attention among wrestling fans. While i don't agree with some of his gimmick changes, i will never forget the character that birthed his extreme career.