Cobra Lords and Darkness Warriors are extremely hard enemies. They hit very hard. When you look at Darkness Warriors, he looks like he has white hair with a red face and using the Warrior set (except the helm).he look like the evil version of the main protagonist in the game and uses the Ghost Sword. The Cobra Lord uses the Battle set with the Severing Axe. They use the same dash skill as the player and can block, unleashing a similar blade wave like the player. The best strategy that I can think of is countering them with high armor and attack, or counter by spamming your dash attack.
An an alternative is to parry his slowest attack, the dash. If you keep him at the edge of your screen he is forced to use the dash attack, and if you block the moment he enters your screen you can parry. After parrying you run to about a screen and a half away (while he's still stunned) and repeat the prosess. But keep in mind the darkness warrior is just as fast as you are, so you can only gain distance in that split second he's stunned.