You gain a +3 bonus to attack and damage rolls made with this magic weapon. In addition, the weapon ignores resistance to slashing damage. 
This is a sythe with the stats of a greatsword.

When you attack a creature 20 on the attack roll, falxcruor steals the blood of the creature. The creature dies if it can't survive without it's blood. A creature is immune to this effect if it is immune to slashing damage, doesn't have or need a blood, has legendary actions, or the GM decides that no. Such a creature instead takes an extra 6d8 necrotic damage from the hit.

 When you hit with a melee attack using this weapon and reduce the target to 0 hit points, you gain 2d6 temporary hit points.

 

Conjure Blood Elemental

Falxcruor holds 5 charges and recharges at midnight. 
If you are holding the sythe, you can use your action and 1 charges to cast the unseen servant spell from it, summoning an blood minion. (functions the same as unseen servant)
If you are holding the sythe, you can use your action and 3 charges to cast the conjure minor elemental  spell from it, summoning an bloodwolf. (check homebrew)
If you are holding the sythe, you can use your action and 5 charges to cast the conjure elemental spell from it, summoning an blood elemental. (check homebrew)

Become Blood

You can use an action to melt into a pool of blood.
While in this form, your only method of movement is a walking/climbing speed of 30 feet. The target can enter and occupy the space of another creature. The target has resistance to nonmagical damage, and it has advantage on Strength, Dexterity, and Constitution saving throws. The target can pass through small holes, narrow openings, and even mere cracks, and an pass through liquid. 
You can use this ability once every day.

 

Curse 

When you attune yourself with Falxcruir for the first time, it burrows in your flesh and dissapears until the end of your short rest. From this point on, you are fused with the weapon and must be in physical contact with it at all time. 
It can be concealed in your flesh using one minute. It takes the same amount of time to get it back out.
It can be attached to your back (or other body part) as an action (Similarly to how you would sheathe a weapon)

For the same reasons, you cannot be disarmed.

If you try to rip out the weapon, it takes a DC 25 strenght check and deals 6d8 slashin damage. If you dont pick Falxcruor withing the next round, you take an infernal wound (lose 1d10 hit points at the start of each of its turns due to an infernal wound. Any creature can take an action to stanch the wound with a successful DC 12 Wisdom (Medicine) check. The wound also closes if the target receives magical healing.)
Furthermore, you gain one level of exaustion.
Every hour and a half without contact, you gain an additional level of exaustion. If you are within dashing distance of Falxcruor at that time, you must make a DC 15 wisdom saving throw to avoid being enthralled to pick it back up.
If you survive 8 hours away from it, you are freed from the curse and falxcruor dissolves into a pool of blood. It regenerates 2d4 days later. 

If a creature picks up falxcruor before it dissolves, it can attempt to attune themselves to it, freeing you from the curse. 

Proficiency with a greatsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Damage, Combat, Heavy, Two-Handed