One Piece's Roronoa Zoro is a master swordsman who serves Luffy as a member of the Straw Hat Pirates. He's a user of the Three-Sword Style, which has been his signature fighting style since early childhood.
Zoro recently got his hands on a completely new sword, named Enma, which was formerly wielded by none other than Kozuki Oden himself. The blade draws out huge amounts of Ryou from the body of the user and thus greatly improves the Haki usage and control of the user. With this sword, Zoro has gotten stronger than ever before. Which One Piece characters would lose to Zoro? Who are still too strong?
10 Can Beat: X Drake
X Drake is a member of the Worst Generation, just like Zoro. He is one of Kaido's Tobiroppo, meaning his power and authority in the crew is quite high. Drake is known to be a decent user of Haki but his biggest strength is his ability to turn himself into an Allosaurus or its hybrid at will using his Devil Fruit.
Although his Zoan Devil Fruit certainly grants X Drake great recovery rate and strength, it still pales in comparison to that if Zoro. Furthermore, with Enma, Zoro's Haki has likely gotten much stronger.
9 Can't Beat: Dracule Mihawk
Mihawk is the One Piece world's strongest swordsman and the person who Zoro aims to surpass one day. Although Zoro has come a long way since the two-year time-skip, he is still nowhere near the level of Dracule Mihawk.
Thankfully, Enma has taken Zoro a bit closer to where he aspires to be but the Straw Hat swordsman still has ways to go before he can actually defeat Mihawk.
8 Can Beat: Charlotte Cracker
The 10th son of Big Mom, Cracker is an incredibly powerful swordsman who wields Pretzel, a blade with an unknown rank at the moment. His mastery over Armament Haki seems quite great as even Luffy couldn't break through it without the raw power of Gear Fourth.
With Enma, however, Zoro's very own Armament Haki is likely gotten much more refined than it was before he trained with it. With that in mind, for Zoro to overpower Cracker shouldn't be impossible.
7 Can't Beat: Shanks
One of the Four Emperors of the Sea, Shanks is a man with a bounty of over 4 billion berries. He rose to the position of an Emperor only 6 years before the current storyline of One Piece and has, since then, established himself as one of the strongest people in the world.
While Shanks might not primarily be a swordsman, he's still exceptionally good with a sword, evident from the fact that he was able to duel with Mihawk in the past. For Zoro, defeating him doesn't seem to be possible at the moment.
6 Can Beat: Jack The Drought
Jack is a man worth a billion Berries in the One Piece world and is one of the three right-hand men of Kaido of the Four Emperors. Using his Devil Fruit powers, he can turn himself into a Mammoth and its hybrid at will and this grants him an incredibly high recovery rate and strength.
Although Jack is durable, Zoro now has improved Haki and the power to cut through most objects with Enma. The sword had made him considerably stronger and in a fight against Jack, Zoro would definitely triumph with Enma in his possession.
5 Can't Beat: Kaido
The strongest creature in the One Piece world, Kaido is a mighty powerful pirate who is said to be unbeatable in a one-on-one fight. He has fought several powerful characters over the years and has taken only a few wounds to date, which just goes to show that he's a cut above the rest.
Zoro is nowhere near the level of a Yonko at the moment and even with the significant power boost that Enma has given him, he's lacking in more ways than one.
4 Can Beat: Killer
Killer is the right-hand man of Eustass 'Captain' Kid and like Zoro, a member of the Worst Generation. He has a bounty of 250 million Berries on his head, which is only slightly lower than Zoro's 320 million at the moment.
Killer is extremely strong, as was evident from his brief fight against Zoro in the Ringo region of Wano Country. Now that Zoro has acquired Enma, he's gotten even stronger than before and his Haki will now allow him to cut even deeper. At the moment, Killer stands no chance against Zoro.
3 Can't Beat: Big Mom
Another one of the Yonko, Big Mom is the world's strongest woman and a pirate with a bounty of over 4.3 billion Berries on her head. She's described as a pirate every bit as fearsome as Kaido and that just goes to show how difficult it is to beat her in combat.
Even with Enma at his side, Zoro would struggle to fight some of her subordinates, such as Charlotte Katakuri at the moment. For him, taking down Big Mom in a fight is, more or less, impossible.
2 Can Beat: Kurozumi Orochi
The Shogun of Wano Country, Kurozumi Orochi is the man responsible for laying waste to Wano slowly but steadily. He is an evil man who bears a grudge against the people of Wano, including the likes of the Kozuki.
Being very close to Hiyori, Zoro understands and shares the pain to quite an extent and would relish the chance to kill Orochi in battle. With or without Enma, Zoro would absolutely demolish Orochi in a fight, although it would be fitting if he wields Oden's very own sword to kill him.
1 Can't Beat: Luffy
Luffy is the captain of the Straw Hat Pirates and the strongest member of the Worst Generation after Yonko Blackbeard. He's a pirate worth 1.5 billion berries at the moment and just like Zoro, he's gotten a bunch of great powers in the Land of Wano to make himself stronger.
While Zoro is certainly strong enough to take on Luffy in a fight, it won't end well for him. In terms of both Observation and Armament Haki, Luffy is superior to Zoro.