Hypostasis can be considered like a miniboss in Genshin Impact. They are bosses that you need to defeat if you are looking for an elemental stones used for character ascension. There are currently 3 Hypostasis bosses, and they are pure element, which means attacking a thunder Hypostasis with a thunder attack will deal no damage.
They all generally work the same way:
They don't take damage from elemental attacks if it's the same element as them.
After 1 or 2 attacks, they will expose their core.
You can only attack them when their core is exposed
When their health gets low, you need to stop their recovery phase.
The recommended element to use is fire, since it works on all 3 of the bosses. If you are having difficulty against them, you can always try it with multiplayer. The respawn time for them is around 5 minutes.
You will need to bring elements that can deal with Electro like fire, or ice to deal with its recovery phase. The electro hypostasis can be a tricky one to deal with because of the area attacks.
When it shoots out lasers in all direction, go into its inner circle and watch the symbol below the crystal, when it starts to vanish, you'll want to run out of the circle to avoid taking damage.
The other notable attack is the electro waves. Simple way of dealing with this is to run far away out of its range, or use characters like Venti, or Geo main character to lift you off the ground.
The electro cage can be easy to avoid once you start seeing the pillars coming down. If you get trapped inside, you can either destroy the pillars, or use Geo main character's elemental skill so you can climb and jump outside the cage.
In the recovery phase, there will be 3 small electro crystals near it. You need to destroy all three with elemental attacks to deal damage. Water will not be dealing any damage to it. If you fail to destroy all 3 of them, it will end up recovering with the remaining crystal(s) when it enters recovery phase again.
The Anemo Hypostasis is arguably the easiest one, since most characters and elements can deal with it, except for wind attacks. If you are feeling unsure, you can get some distance from it and run around because its attacks aren't difficult to avoid.
You'll want to always get some range between you and the Anemo hypostasis because one of its common attack is to suck in surrounding players and explode to deal damage. If you get sucked in by the small area, you might not be able to escape the pull, so you'll either have to switch to a different character to take the damage, or time your dodge for the invulnerability frames.
Similar to Eye of the Storm's attack, the Anemo hypostasis can create multiple small tornadoes surrounding it. It's fairly easy to avoid since the tornadoes aren't big.
When it enters stationary mode, it will try to absorb the Anemo energy that's left in the air. Once absorbed, it will deal wide aoe damage. You can prevent it from doing this by taking the orbs before it by flying up when it releases some upcurrents, otherwise just run very far from it to not take damage.
During its recovery phase, there will be Anemo orbs floating around it. Simply fly and take all of them as soon as you can.
In order to reach it, you can go to the small island on the right of the teleport waypoint, then go to the other island without swimming. The Geo hypostasis is the sturdiest one of them all. In order to deal damage to it, you have to destroy the pillar that it is on, then it will drop down with the core exposed for you to hit. So it's recommended that you use a character that can use a claymore, because there's a lot of pillar breaking in the fight. You can use Geo main character to deal some damage from the elemental skill, but that can be a very slow process. Ningguang can also work to destroy the pillars, but you won't be able to deal damage to the core.
One particular attack that is hard to avoid is his long range snipe. When you notice a circle around your character, the Geo hypostasis targeting your for its attack. If you are not good at using dodge for the invulnerability frames, switch out to your tanky character to take the hit.
As you're attacking the pillar, you might notice the Geo hypostasis is shooting a laser down the pillar, a light will start showing up on the pillar going down from the top to the bottom. Once it reaches the bottom, there will be a wide ground attack. It can come out pretty fast, so it's best to get some distance when you see the laser.
Most of its attacks can be avoided easily, but there is one particular move that you have to be mindful of. When it starts to channel using all the pillars, causing quakes every second to deal damage, you need to find the floating fragment near a pillar and destroy it. This will give you a shield to prevent taking damage from the quakes.
During the recovery phase, you simply have to destroy the all the pillars before it's done. This can be difficult to do by yourself, especially if you are lacking damage. But rest assured, if it recovers, you just have to knock it back down to recovery phase and it will only create the remaining pillars that you didn't get to destroy before.