In the beginning of the Dressrosa arc Luffy enters a championship to win his late brother's devil fruit, the Mera Mera no Mi. During the even in the Block B battle, Elizabello II uses his king punch to pretty much take down everybody (except Bartolomeo).
What is the origin of Elizabello's power? Does he use a devil fruit or is he born as an ancient weapon (like Pluton or Poseidon aka. Shirahoshi? Or is that simply physical strength?
It is simply physical strength... combined with flair put in by Oda.
There are a lot of odd abilities in one piece that are not devil fruits or have any real explanation. Sanji legs catch fire and don't burn him. Zoro makes tornadoes. Fishmen summon water from thin air. The king's punch is odd in our world but, there, it is just a very strong punch that takes a lot of focus, warming up, and talent to use.
There doesn't appear to be any haki, devil fruit, or weapons.
