Royal Revenant may be one of the easiest minibosses in Elden Ring, at least once you know the trick. Although it doesn't count as undead, it takes massive damage from healing spells. The first hit deals half its health and breaks it stance, giving you plenty of time to cast it again and finishing off the Revenant. The earliest Heal spell you can get can be equipped by any class with a few pieces of equipment that buff Faith, so this fight can be absolutely trivial for anyone.
Given that, it's a little surprising how much attention was put into its combos. The chart on its own is fairly complicated, particularly because of the Revenant's habit of teleportation:
But this actually represents a simplification of the actual AI. Many of the moves that are represented above as a single box actually have multiple different animations with only subtle differences between them. Since each of these animations combos the same way, I was able to combine them and produce a more comprehensible graph, but the original version was much messier.
Why does it have so much duplication? I think the answer is simply to make sure that the animations flow fluidly between one another. For some of them, this is a practical necessity: if the "teleport away" animation makes the model invisible, the "swing" animation that follows it must make the model visible. Some are more aesthetic, like making sure the animation begins with the model's arms in the right place to avoid unsightly automated tweens.
The result is impressive. Although Royal Revenant is a fairly minor boss, it (and its mob form) makes a strong impression, with its relentless pressure underscored by the fluidity of its animations. When you first fight it, it feels like it's doing one huge combo, and this attention to detail is why. In a game like Elden Ring where a core part of the challenge is learning to read and react to a boss, conveying visual information isn't just aesthetic, it's part of the way players play the game.