The first thing you'll notice when you go through the fog gate is the lava; do not touch this at all, as it is very dangerous and will quickly deplete your health. Now, when the fight starts, the first thing you want to do is go to the right until you reach an open area that has a corpse with some loot on it (2 Green Titanite Shards). This area makes it much easier to fight without having to worry about being knocked into the lava. You can cut off its tail, but the tail doesn't die and requires a few extra hits to kill it; if you do this, you get the Orange Charred Ring, which allows you to walk on the lava while taking very miniscule damage (you also get it if you defeat the boss without cutting its tail). The first attack you'll most likely see when fighting this boss is its long range attack where he shoots out one of its arms at you; you can dodge it by rolling to either side. His most dangerous attack is when he leaps into the air and tries to land on you or either slams its one arm on the ground; it's best to roll away from it at this point. If you stay under his legs for a while, it will stomp the ground with both legs, so make sure to move away if you see it doing this attack. It seems to get a small explosion when it jumps up into the air once its health gets lower. It also seems to be able to grab you and deal big damage, but it doesn't seem to use that move too often. As long as you stay kind of underneath him and hack away, you should be able to defeat him without too much trouble; stay away from the lava!