Genshin Impact
Cryo Hypostasis, strategies, weak points, and achievements
Defeat Daleth, the Cryo Hypostasis locked behind an infamous quest in Dragonspine.

Daleth is a Cryo Hypostasis that you can fight in Dragonspine; since it is made of Cryo, it is immune to the element; defeating it will reward you with Crystalline Blooms and Cryo Gems. So far, only two characters need Crystalline Blooms, and one of them is no longer available.
Cryo Hypostasis Location

Cryo Hypostasis Arena

How to Unlock the Cryo Hypostasis Boss Fight.
To be able to fight the Cryo Hypostasis, you have to complete a long quest called In the Mountains, obtained at a camp by the foot of the mountain, and unless you have Dehya, you'll need lots of healing, as she is the only one whose auto-healing is higher than the HP Loss from Sheer Cold.
After beating the Quest, the Cryo Hypostasis will appear in the shown location.
Strategy
Being close to the Cryo Hypostasis will considerably boost the Sheer Cold Gauge, so try to stay close to the heat sources at the Arena's edges.
Daleth is open to your attacks during or right after they end. Watch carefully and pick which moments are more accessible for you to attack.
The Boss' attacks will either leave a distance between the both of you or need you to stay far, so a ranged character is recommended.
At the end of the fight, the Cryo Hypostasis will raise a Cryo Shield and fire three spiked balls at you; if you are close to the boss, the balls will not fall too far apart, and you can throw them back with charged attacks (aimed shots with bows also count, even if not fully charged) from the side opposite the Hypostasis, breaking the shield will stun the boss for a short while.
Weak Point
This boss does not have any specific weakness nor weak point and technically is equally resistant to all Elemental and Physical attacks besides its immunity to Cryo, but since it is made of Cryo and is always affected by this Element, Pyro attacks will be more effective, as they will generate Reactions.
Achievements
"...A Single Night's Work"
Defeat a Cryo Hypostasis that is in a weakened state.
After breaking the shield in the last phase, defeat the boss before it gets back up.
"Knee-Deep Snow..."
Defeat a Cryo Hypostasis that has revived three times.
Let the Cryo Hypostasis regenerate in the last phase; do it three times in the same fight before defeating it.
Put on Ice
Defeat a Cryo Hypostasis in Co-Op Mode.