The Sentinels are a 1-phase fight with an intermission.
Main Phase
The fight will start with the raid split into two groups. The odd/left group will begin with the venom sentinel and the even/right group will begin with the blood sentinel. Each sentinel has two abilities, a tank buster, and a passive stacking damage aura.
Venom
The venom sentinel is closer to an add fight with things around the arena to deal with.
Periodically, the sentinel will drop tiny slimes around which need to be stepped on. Don’t take more than two soaks before letting your dot fall off.
Twice per intermission, the sentinel will summon a large slime that deals continuous raid wide damage and needs to be killed quickly. The tank should stand the sentinel on top of the slime for cleave damage.
Tanks should watch out for Empowering Slam and save defensives for such. Each cast gives the boss 10% extra damage until the swap.
Blood
The blood sentinel focuses more on dots, but slimes from the venom fight will still end up on this side.
Regularly, the sentinel will apply dots to random players. Healers should dispel these as soon as possible.
Twice per intermission, the sentinel will start a large group soak. All blood players should be inside the soak to spread the damage.
Tanks should watch out for Bloodvenom Injection and save defensives for such. Despite appearances, it does physical damage, so armor applies. The dot it leaves will inflict a lot of damage, so care has to be taken when nearing the intermission.
Intermission
After 4 tank busters with 2 big abilities, (Roughly 20 stacks of aura) the sentinels will go into the middle and equalize their health. Tanks should immediately taunt the other sentinel, while dps should hold damage (The bosses are 99% resistant during this phase).
You will have four orbs over your head, a combination of 1-3 red with the rest green. You need to find someone with the inverse combination and run into them to remove the dot. (Ex. You have 3 red and 1 green, so you need to find someone with 1 red and 3 green.)
Once the intermission is complete, go back to your side while the tank brings in the opposite sentinel. Incoming damage will be highest at this point while the aura from the other boss falls off, and tanks need to be extremely careful until they take their first tank buster.