Consumed King's Garden

This location is accessible after you've faced off against the Dancer of the Boreal Valley. There are two ways for you to go from here. The ladder in the boss chamber leads to Lorthic Castle, which you will be visiting later. For now however, go back outside via the western path and step onto the higher walkway; past the locked door here is a Cathedral Knight for you defeat as well as some remains that has some souls. Eliminate the Cathedral Knight and use the lift behind him to reach the Consumed King's Garden.

Once you're on the descending elevator, hop off onto the first platform that comes into view then go down the stairs to the right where some remains with an Estus Shard can be found. Go left from here to see a spot that you can drop down for a Titanite Chunk. Drop further down onto the poisonous stuff and make haste toward a safer spot, and you may want to have a look at the opposite end of the building that the elevator was in to grab the Ring of Sacrifice. In any case, your next destination is the big elevated platform that has a Cathedral Knight on it.

Kill this enemy and you will have the option to either move on with the level, or try to secure all the loot that those three intimidating monsters are guarding. Should you decide to try and deal with the enemies, I would recommend using a fire-based weapon as hitting them with said element causes them to recoil if only briefly. Thereby giving you the opportunity to rush in and do damage. Do this until all of them are gone and take care of slug horde to finally clear out the area. Now you can safely go and collect the loot here including some Black Firebombs, a Claw and a Shadow equipment set.

Back on the elevated platform, go left to look under the stairs for a Dark Gem then go on up to find a Titanite Chunk. At the other end is a platform with a couple of corpses beyond it. One is carries a Titanite Chunk and the other has some Human Pine Resin. Go through the doorway nearby and use the lift to reach the top floor. The room beyond the hallway here has some Thralls and Clerics waiting. Clear out this area before dropping down beneath an overhang to collect a Titanite Scale. Climb back upstairs afterward to grab the Titanite Chunk next to a door. Beyond this door lies a shortcut to Lorthic Castle.

Return to the elevator and get off on the platform about halfway down. Follow the path here to a Dragonscale Ring. Now at the large open area, you will find a pair of Cathedral Knights as well as a Hollow Cleric. Defeat both of the knights and the second one fall will drop a Magic Stoneplate Ring. Move along further down the path beyond to your next boss encounter, this time against Ocerios, the Consumed King.

Boss Battle - Ocerios, the Consumed King

The first thing I'll point out is that Ocerios is an ice monster, whose white breath attack can sometimes freeze your character (and inflict Curse if you're hit by it enough times) in addition to doing a good amount of damage. Equip a lightning-based weapon or use Gold Pine Resin to add said element to your attack and run up next to his legs and start hitting him. Ocerios also has a nasty tail swipe attack that can be deadly if it hits you consecutively. Either roll away out of reach of the tail or use Estus Flasks to heal.

You will receive a soul and the Ocerios, the Consumed King trophy upon beating this boss. Light the bonfire in this area before moving on.