The Phantom Stalker
The Phantom Stalker is a huge creature found in Blackwhisper Cave. You encounter it only once. You disturb it when you cause an earthquake in the main story of the game. It wakes up while you try to run out of the cave and attacks you.
It is one of the most powerful enemies in the game because of how much health it has and the damage it deals. It has very quick and armor piercing attack where it hits you with its enormous tounge. Its tounge absorbs your health, healing itself.
Because of the earthquake, you have 2 minutes to kill it or you both die.