This is the vampire.
This mob will spawn in any biome except for the nether. It needs a low light value to spawn and burns in the sun.
When they die they will spawn a vampire bat.
They do 2 hearts of damage when they hit you.
It drops vampire blood. Vampire blood is pretty important in Goblins and Giants. You can craft it into redstone like this.
You can craft bloody giant bones with it as well.
These bones are used to craft Bone Spears.
The last thing you can do with it is craft poison bottles like this.
Use these poison bottles to craft Poison Swords.