Rewards: 3100, Frozen Needle (in the chest found in the room beyond the boss room)
Spirit Summons Available: Yes
The Royal Revenant is a royal pain in the butt. Its attacks are fast, it can disappear, it can poison you — and it’s straight-up nasty to look at. Luckily, there are a number of ways to handle it that aren’t too tough to pull off. In this guide, we’ve got two different strategies for dealing with this boss.
With either strategy, Spirit Summons can help quite a bit. You can spam the summoning button as you enter the room, and usually, the boss’ first attack will miss. If you want to be extra careful with your HP, you can follow the strategy below, but during the first opportunity to attack, summon your spirit(s) instead.
Strategy 1: Casting Heal
Being a disgusting monster, the Royal Revenant is naturally affected negatively by holy magic like healing spells. If you cast Heal or any other AOE healing spell (i.e. spells that can affect allies as well as you), and the boss is in the area of affect, you’ll take a huge chunk out of its health bar.
If you’re using Spirit Summons, then you can simply wait until the boss is targeting your summon and walk up next to it and cast heal. Otherwise, you’ll want to wait until the boss is using Poison Spray, or else get near it as it ends its Flailing Advance, in order to successfully land your heal spell on it. It should only take a couple of casts to completely finish the boss off.
Strategy 2: Using a Shield
The other easy-to-use strategy is equipping a shield that has 100% physical defense (such as the Beast Crest Heater, which can be grabbed in Limgrave without much trouble). With your shield equipped, you can block all of the bosses attacks except for two: the Poison Spray and the Flailing Advance. Both should be rolled out of (you should roll past the boss instead of sideways or backwards). These attacks also happen to be the two safe windows to attack the boss. Either during or immediately after the Poison Spray, or during/after the long flailing attack, the boss can be safely damaged.
The move where the boss flails its arms and moves rapidly forward is your best chance to attack, but you must strafe or roll to get it to go past you
If using a melee weapon, you’ll want to follow the Revenant as it goes past you in order to deal some damage
The Poison Spray has a long animation, and cannot be blocked, so run or roll horizontally to get out of the poison. Once you’ve gotten out of the area of effect, you can run up to the boss and do a jumping attack, or cast a spell/shoot your arrow if you’re using a ranged build.
Remember to block after attacking!
The boss only has 2 attacks that will stagger anyone with a reasonable amount of stamina, the Big Hug and the Flailing Advance (which are often seen in that order). These attacks should generally be rolled through (although the Flailing Advance can be blocked circle strafed away from if it isn’t preceded by the Big Hug).
The Big Hug seen twice, with both of the common follow-ups (the second Big Hug is chained into the Flailing Advance)
Ideally, roll diagonally towards the boss, so followup attacks are more likely to miss — you should also immediately start blocking when you come out of your roll. The rest of the boss’ attacks can be safely blocked — just make sure to let go of block in between combos to regain your stamina. You should always be circling to one side, as this will make many attacks miss, therefore saving you some stamina. Note that you can roll even if the flailing attack is already hitting you.
Moveset
The boss has a lot of hard-to-differentiate attacks, so instead of listing them all, only the moves relevant to the strategy in this guide are listed here. Any move not listed can be safely blocked.
Poison Spray – The boss stands up and sprays poison in a cone in front of it.
Big Hug – The boss stands up and spreads its arm (and its stomach-mouth), then leaps towads its target. Frequently chained into the Flailing Advance.
Flailing Advance – The boss swings wildly with all of its many arms and scrabbles forward.
Unabashed FromSoftware fanboy still learning to take his time with games (and everything else, really). The time he doesn't spend on games is spent on music, books, or occasionally going outside.
3100, 
