Background
A Royal Revenant encountered in the hidden cellar of Kingsrealm Ruins in north-western Liurnia of the Lakes. It guards a chest containing the Frozen Needle.
Strategy
Encountered in a very small room and without having to go through their signature lengthy spawning animation, this Revenant will turn aggressive quickly.
If it leaps towards roll forwards to the left of it and get in a hit before backing away, being ready to roll. Should it start to use more short-ranged melee slams, back away to provoke more leaps. Sometimes it will start to chain these slams into one long combo, either try to keep as far away as possible from this or get behind it if already close.
Occasionally it will start to emit a green color around its head which signifies that it's about to spit out a thin cone of Poison sludge. Potentially dangerous if caught in the middle of an action such as drinking a Flask of Crimson Tears but otherwise easily rolled or jumped away from.
Sometimes it will slip through a portal underground to appear behind its target and spit poison before starting its attack routine again.
Healing incantations
One easy way to kill it is to find an opening to cast a cheap healing spell such as Heal and then cast it again immediately while it's stunned. Any class can do this as even a Prisoner has enough Faith with a Commoner's Garb/Commoner's Simple Garb and Two Fingers Heirloom.
Another way to do this is to summon the Finger Maiden Therolina Puppet, though she's more unreliable in casting her healing incantation.