8: Anemo Hypostasis
The easiest Elite Boss is the Anemo Hypostasis, but don't let that get you thinking that this boss is easy. It can easily kick your crap in if you're not careful. Not only that but you also have limited windows to actually get damage in on it, which is also true for the other Hypostasis bosses too. This means you'll have to focus on dodging and keeping your party healthy until you can get ample opportunities to chip away at its health. However, with enough practice you'll find that its attacks aren't terribly difficult to dodge. The only attack that can be a problem is an AOE that covers over 2/3s of the arena, but if you know when it's coming you can dodge it every time. It's definitely not an easy boss, but it's not one that should force any massive changes in your party either.
7: Electro Hypostasis
From one Hypostasis to another, the electro variant is a bit of a double edged sword in its difficult. It has some of the deadliest attacks between the 3 Hypostasis, but it also has gives you the largest windows of attack out of the 3. So while I do find its attacks more difficult to dodge than the anemo, I often find myself ending the fight rather quickly. Granted this could be because my Xianling is a dps machine, but I digress. The main reason why it ranked above the anemo however, is because of the attacks. Some of them can be very difficult to dodge such as a 3 combo attack that can desimate your health bar. Again, definitely not easy, but no super difficult either.
6: Geo Hypostasis
Tired of the Hypostasis train yet? Well too bad! I should note though that I find this one to be much more difficult than the other two. When you first begin the fight, it immediately opens by creating 5 Geo pillars, 1 in the center, and 4 on the sides. The thing is that it really likes to stay up on those platforms, and some its attacks thrive off of those platforms, including an earthquake AOE that covers even more real estate then the anemo's. I should note that if you do break the platform that its on, you will be given an ample opportunity to sink some damage in on it, however, there are 2 problems with that. 1st, the platforms do not go down easy. Even when you're using a claymore character, you'll find that they don't go down easy at all, and 2nd, it's teleport habits. Unlike the other two hypostasis that only teleport for a single attack or two, the Geo Hypostasis is incredibly teleport happy, to the point where it will feel like it will teleport after every other attack. This all forces you into 1 of two strategies to take it down. 1: Camp in a place where the earthquake can't hit you with a bow character, or 2: use a claymore character and try to take down the platform it's on in order to get good dps. To put this fight short, bring a claymore character and either a bow character, or your pest melee dps.
5: Pyro Regisvine
We now enter the top 5, and from here one you're probably gonna need to do at least some sort of party switching if you want the optimal strats. The 1st thing you should know about this boss and its Cryo sibling are its weakpoints. In both fights they start by exposing the on at the bottom stem, then the one on their face, and so long as one of these is active, your damage against it will be incredibly miniscule. Another thing to note is that the shields will only go down optimally if you use the right element against it, otherwise the weakpoints will feel like damage sponges that take an eternity to destroy. Once they do break however, you'll be given a decent amount of time to sink in damage. So what's the optimal strat against this? One word, Barbara. Barbara is a FREE Hydro mage that is more on healing than actual damage, but the catch is, the damage doesn't matter against the weakpoints. No joke, you could be dealing SINGLE DIGIT damage against them and you'll still cut through them like butter. Once it's down, swap to your dps and whale on it. Rinse and repeat until the boss is dead.
4: Cryo Regisvine
Most of the things I said about the Pryo Regisvine apply here as well, with the only major differences being attacks and elemental matchups. Key note, those difference are what make it more difficult than its pyro sibling. Unlike the Pyro one where you had an easy answer against the weakpoints, here you don't have that luxury. Your best FREE option is Amber, who is a meme and garbage, other than that, you're forced to play the gacha and hope for either Diluc or Xialing (you can also get Xianling by beating the third floor in third chamber, but good luck beating that at level 30. I beat it at 30, and it was very painful), but even then both Diluc and Xianling struggle to reach the weakpoint on its face. On top of that you also have to deal with the freeze status, which is easily the most annoying of the statuses. All of this blends together to be a quite difficult boss.
3: Oceanid
This is probably my least favorite elite boss, mainly because the very majestic thing flying around the arena, the creature that is suppose to be the boss, rarely every attacks. Instead it summons these annoying water underlings that do the dirty work for it. This boss beats the rest of the pack for a couple reasons. 1: The minions regenerate health and do loads of damage. 2: The arena shrinks as the fight goes on. And 3: the one attack that Oceanid actually does. If you take too long Oceanid will create a water attack beneath you, which is inescapable and insta kills whoever you have out. These 3 things make this boss difficult and very annoying. Just spam electro and cryo and you'll win.
2: Stormterror/Dvalin
The final boss of the monstadt arc and my personal favorite of the elite bosses, Stormterror/Dvalin earns its spot at second place. It's got deadly attacks, small windows of attack, and a health bar to suit a final boss. However, the biggest thing that puts it at 2nd place is the removal of platforms. Similar to Oceanid, Stormterror/Dvalin will delete certain platforms during the fight. However, unlike Oceanid who does it at certain points of its health. Stormterror/Dvalin does it at regular intervals and will continue to do it at those intervals, meaning if you take too long you will run out of safe platforms to go on and will likely have to restart the fight. All I can say is good luck.
1: Lupus Borealis
The hardest boss in Genshin Impact is Lupus Borealis. Basically take everything that made the previous bosses difficult, and that's what this fight is. He has it all. Freeze status, limited windows of attack, a massive health bar, absurd damage, and arena covering attacks, all of which is topped off with a second phase that cranks everything I just mentioned up to 11. Like with Stormterror/Dvalin, all I can say is good luck, you're gonna need it.