Because you are a blood elemental, your true body is liquid, giving you the ability to fit through spaces as narrow as 1 inch without squeezing. During combat, you can use your true form to enter an enemy’s space. When in your true form, you have immunity to being grappled or being considered prone.

While occupying an enemy’s space, you can attempt to use your Life Drain ability, all creatures aside from yourself within your space must make a DC 15 strength check, on a failure, they will take 1d10 necrotic damage (Increased to 1d12 at level 5, 3d6 at level 8, 2d10 at level 12, and 2d12 at level 15). When this happens, the creature’s blood is drained by osmosis, and you gain half the damage dealt as temporary hit points. The number of times you can use this per long rest is equal to a D6 die rolled when the rest is taken. Each long rest gives a new roll, unused charges of the ability DO NOT carry over.

As a ritual, you can take 6 minutes to inhabit a corpse of a creature that is size medium or large, draining its blood, and replacing it with yourself. The creature must have had blood when alive, meaning you cannot inhabit constructs, skeletons, or other non-juicy creatures. The corpse must also be relatively fresh, and unrotted. Using this ability is similar to the druid Wild Shape ability, meaning that your flesh suit has its own durability pool, this is determined by rolling 2d10+3 if it is a medium creature, or 3d10+5 if it is a large creature. Inhabiting a corpse with missing limbs or other significant damage subtracts 5 health per detrimental wound. (So if you inhabited a human corpse with a missing arm and rolled a 15, the corpse would have 10hp before it became unusable) You CAN reattach missing limbs, but you must use a long rest devoted to each limb individually to achieve it. The Corpse cannot be healed, and upon breaking, you are stunned for a round, when your turn comes back around, you can choose to exit the corpse and consume your whole turn doing so.

Darkvision

+1 to any two of Charisma, wisdom, strength, or constitution. As well as a -1 to dex.

As a blood elemental you are immune to poison damage and conditions, along with exhaustion. In your true form, you are also immune to the prone and grappled conditions.

You are weak to cold damage. It does not deal extra damage to you, however, when you are damaged by something with the ice or cold property, you will lose 10ft of movement until the end of the next round. When in your true form, you are weak to thinners, such as water, alcohol, etc., when thinned, you have disadvantage on all dexterity and con based checks.

You can understand Common and 2 other languages. HOWEVER , in your true form, you cannot speak at all. To be able to speak, you must be inhabiting a corpse that itself has the ability to speak. You cannot, say, be inhabiting a corpse that has had its throat gouged out and try to speak.

I think it won't let you play the race if it says your size is large, so just keep it in mind that your size, playing this race, is large when outside of a corpse.