Silvers Rayleigh is the former first mate of the Roger Pirates, known as the “Right Hand of the Pirate King”. Rayleigh knows the “True History” of the world from his time with Roger.
He is extremely powerful, easily one of the strongest characters introduced.
Rayleigh is an enemy of the World Government. He is one of the few people who know the true history. He was willing to tell Robin about the Void Century, but he was interrupted by her. The Government considers such people as a great threat.
Based on this, Rayleigh should easily have a bounty higher than 1.5 Billion Berries.
Kuzan is one of the most powerful Marines of his generation.
He was nominated by Sengoku for the position of Fleet Admiral. However, after losing the position to Sakazuki, he resigned from the Marines and affiliated himself with the Blackbeard Pirates.
8-Marco the Phoenix
Marco the Phoenix is the former 1st division commander of the Whitebeard Pirates led by the Yonko Edward Newgate. He was Whitebeard’s closest confidante and his right-hand man.
He’s now the leader of the Whitebeard Pirates.
Dracule “Hawk Eyes” Mihawk is a world-famous pirate who currently holds the title of “Strongest Swordsman in the World”. He was one of the Shichibukai — the first revealed and formally introduced — until the organization’s dissolution.
He is one of the most powerful pirates to appear so far, possessing an immense amount of skill in battle.
Due to the Shichibukai system being obsolete, he is now once again an enemy to the government as the Marine waste no time trying to arrest him. Mihawk, however, does muse the fact as he is eager to fight against them.
I believe that, since Mihawk used to duel with Shanks, his bounty is near the “level” of a Yonko.
The most prominent feats of Teach’s power was defeating three commanders of the Whitebeard Pirates: Portgas D. Ace, Thatch, and later during the Payback War, Marco, the new Captain of the Whitebeard Pirates. After the time-skip, he and his crew fought against the Revolutionary Army and destroyed their base. It is also stated that they briefly fought against CP-0.
After all of the threatening things that Blackbeard has done to the World Government he has earned a bounty of 2,247,600,000 Berries.
Blackbeard is the most recent Yonko, that’s why he has the lowest bounty among the Four Emperors. He’s the new power that replaced Whitebeard, and he’s still growing.