GauntlikEditThis guardian does "paper, rock, scissors"
The trick to this fight is knowing the weak spot, which will be easy to tell once you target him (Tab, by default, the targeting reticule centers on the red part). After that, it is a matter of waiting for the right times to strike and avoiding damage in between. It is recommended to bring ranged weapons, or the Transmute Metal spell, wearing him down eventually.
From the Prison Gate, go up one screen using the ladder, then enter the purple "boss" door. From the ledge, drop down onto a platform.
You can avoid most of his attacks.
- Rock: Immediately run to the far right. As soon as he shows up over your head, start running left. He only attacks 5 times. If you time it right, he'll miss all 5 before you get to the leftmost end of the platform.
- Paper: just run to the center of the platform. As soon as the lightning starts, just walk left and right accompanying the empty space between two lightnings. It may take some tries for you to learn where the empty space is in the beginning, but you can accompany the central empty space without taking any damage.
- Scissors: If you wait until he's nearer to the center, you can time a jump to the right and only take one hit, and end up to his right, with access to his weak spot. Or go to the left side and use a phase scroll to go behind gauntlet and attack his weak spot. You use the phase door scroll to teleport to the other side of him without taking damage. (Also useful for the challenge)
As for damaging him, what I did was: I targeted him (if he is in the air, you can jump to target him. Remember that the weak spot is in the red part.
- When he was doing his rock, paper, scissors, I'd just spam fire bolts or arrows.
- During paper and rock phases, I just tried to not take damage.
- During the scissors phase, I tried hitting him from behind with a mace. Bow works wonders too.
The best spell you can have for this fight is phase door, except for paper when it's useless. An axe or polearm is best for hitting him while he does scissors.
An alternate approach which makes it very easy is go with full bow skills with the windbreaker (two long arrows per shot). With Bow Mastery 2 (stack x4) it's as easy as it can get. If you know his patterns and buy a few phase door scrolls, you can even attempt the damageless challenge.