One that stands out is the "grotesque". This characteristic feature of Southern Gothic is not necessarily a monster, nor something out of this world, but a really sensitive behavior that moves our insides to hating the character. In this case, the protagonist was mean to Sucker every time Maybelle was mean to the protagonist. So, in him we see the seething anger of humiliation and the pleasure in humiliating others, so cruelly that it makes you feel disgusted at his attitude. Grotesque is the equivalent of naturalism: Very cruel reality.
Suspense and the touch of the supernatural is another one: Something happened to Sucker after Pete did his biggest yelling and humiliating tantrum. But, what was it? How come his eyes became so narrow that it transformed his gesture to that resembling an old man? What is Sucker's real problem?
The third would be the inevitability of fate. Sucker was meant to have a harsh life because even as he was a baby he was hit by tragedy when his parents got killed in a car accident. In Gothic lit, there will always be an element of inevitability that will send a character spiraling down. As we know Sucker changed, but for the worse. There is nothing dynamically changing in his life, nor does there seem to be light at the end of his tunnel.