Oh shit. I think I figured out King's secret.
King's unique power is absorbing attacks. That why he's hard to damage. He just have to activate that power. That explains why Marco damaged him (made him bleed). Zoro did the same he first attacked him at the beginning of the battle.
Zoro hit King with his death lion song.
That is one of Zoro's strongest attacks.
After King was hit his flames behind his head appeared to increase in size.
His attack in this chapter was much stronger than chapter 1032.
That power came from absorbing Zoro's attack. The flames growing in size behind King's head represents King absorbing attacks.
We saw the same thing after King was hit by dragon twister. He blocked it but because it still hit his body he absorbed it.
Look at the size of the flames.
Look at the following scenes
In all those scenes King used a tremendous amount of power. He used so much power he was able to overpower Zoro. King used that power after he was hit by Zoro.
He even exploded immediately after Zoro hit a certain spot on his body
If all of this is true then there's 2 possible ways for Zoro to defeat King.
1 - hit King with an attack so powerful it's too much power for him to absorb and the attack damage him.
2 - hit King with an attack so powerful it oveloads his absorption power causing King to unintentionally explode and damage himself.
What does everyone else think?