Oceiros is an extremely aggressive boss located in the Consumed King’s Garden. The fight starts out slow as a monologue plays, but ramps up as the fight wears on. Be prepared for some erratic, but mostly predictable moves from this boss. When you first enter the fog, move towards the boss and bait him into attacking, rolling forward through his swing and hitting him a time or two. Repeat this process until he holds his staff up in the air and summons crystals out the ground in front of him, which is your que to back away until they are gone. Be sure to be careful, as sometimes when attacking him he will hop backwards and swing, hitting exactly where you will be standing. After roughly 1/3 of his health is gone, he will pause for a moment and then he will get down on all fours like a beast and become aggressive. Getting positioned after this transition is the key to this fight. It’s very easy to get killed here while you are closing the distance, but after you get up to him you’ll want to get him caught in a combat loop of sorts.
Get up to him, keep your shield up and roll through his attacks when you get close. Believe it or not that was the hard part. The strategy now is simple roll through his swipes, and get into his stomach. Swing a couple of times, then block or roll forward as he will charge and do 5 or 6 swipes as he lunges in a straight line that takes him quite far. You must sprint over to him and close the distance as rapidly as you can. Get a couple of attacks in if you have time, but as soon as he lifts his tail, he will do a tail swipe that hits nearly 360. When he does this roll into him and attack once or twice. You will simply be repeating this combat loop now.
Attack a couple of times, block or roll, he will charge and you will chase behind him, get in an attack or two and then roll. Problems arise when you break this cycle, by either not closing the distance fast enough, or by getting knocked down or thrown off rhythym. If you get to far he may charge and one shot you, or may do a quick fly by with his White Dragon Breath that will kill you if it hits.
If you can stay focused, you will have no trouble. .
As found on Youtube