I have been reading the forums regarding various experiences with the Sentinel. I decided to post a new thread to avoid any necro’ing. The fight, I think really isn’t that bad… but needs some minor tweaks. I don’t mind the summons, the crystals, his nova or his speed. The thing that irritates me about this fight, with my conjurer specifically, is the unavoidable stun that lasts for 3-5 seconds every time a meteor, nova, or melee attack hits me. They do not 1 shot me, but I die all the time because I can’t move until everything dog piles me, and by then It’s all over but the crying. I can’t stop to cast at all really, or I get hit, stun-locked and exterminated. It doesn’t bother me that much, I managed to kill him on veteran and Elite and I soloed Ultimate all but him with little problem. I would just like to get this out there on the forum so maybe it will help the devs decide how to better design the fight, I don’t want it easier… I just want a window of opportunity to actually complete it. I would suggest maybe removing the stun from 1 of his abilities, but certainly not all. For all i care, The Sentinel can stay down there and die of old age for the time being.
I finished this as melee and noticed no stuns? Perhaps it’s just a range mechanic and if it is…you are range, you have ample time to move.
Well, I have a summoner myself, a build similar to Pokémon 's. I have cleared all content with it, all nemesis(Iron Maiden included) and the Sentinel. What I’ve found on that fight is that he somehow turns the pets against me sometimes, but he’s doable. As for stuns, I think only his ground shake thing does stun, but you can predict it and dodge.
What’s your stun resistance?
I can not remember I was stun by Sentinel on my pet build nor in Crucible fight
Sentinel fight: https://www.youtube.com/watch?v=FyXGI6Ky3Bk&list=PLocI8CR9wDKXL7YKvsGUXZAvwRW63Ht6C&index=4
Yupperss! Same issue here. My pets problem is even worst. There must be a solution.
Hi 
I’m a conjurer summoner 74 playing in Elite. Kill the Sentinel was my fight to achieve all the quests in Elite.
Like you, I had a lot of difficulty to kill him (4 trys and 4 deaths in 3 seconds…) because I understood too late that the key in this build (pet summoner) is to maximise pet stats. So my gear was not OP to kill him. I’m an active player and love to hit mobs in melee
So my character is weak because my stats are a melting with Chaos/vitality dammage and pet stats.
During this fight my pets had 141% life and 349% dammage. Using Hellhound, Briarthor, Cockroach (trinket pet) Primal Spirit and the pet of Bond of Bysmiel (devotion).
SOLUTION :
Open the door fight but stay behind. Send your pets pull The Sentinel.
He will rush you but cannot because door will close :D.
Now go on the hight of the stairs (in front of the close grids) at the left side. It will permit to you to escape from 80% of his area attacks and you will be able to cast your spells ( CoF, Doombolt, Vines …) during your pets attack him.
Click always in front of the grids when you say to your pets to Attack, not on the sentinel !
Sometimes he goes back… so approach to the grids and go back on the top of the stairs when he rushs you.
After some regen of his life he will not regen and you’ll kill him. The key is to be patient !!!
Killed on the first try whith this technique on 7 minutes. 3 Energie and health potions used.
Sorry for the mistakes and the grammar. I’m French.
Good luck weak summoners 
What? It’s ridiculous, at 75 level you get access to best items that fit to conjurer build, your pet damage must be at last 3 times more, than rubbish 300% (with some skills and potions 4 times more, at level 1200% approximately)
Interesting, but useless, at elite sentinel are cute and plush, he can’t deal damage, he can not do anything else but to die from the fangs of your pets.
he becomes real spines in the ass only on ultimate