This cruel looking bastard sword is broken up into 15 distinct shards of black iron. Despite the obvious separations, the weapon still holds it's form when swung. Even when shards are missing, the rest float in place relative to the hilt.

You gain a +1 bonus to attack and damage rolls made with this magic weapon.

You can pull individual shards from the blade without damaging it, although attacks made with the weapon when it is missing one or more shards are made with disadvantage. Attacks with this weapon cannot be made if more than 10 shards have been removed from it. Each shard can be used as a non-magical dagger. You can use an action while holding the hilt to recall all removed shards, which then instantly but harmlessly return to blade. 

The weapons has 2 charges. As a bonus action, if the weapon isn't missing any shards, you can expend a charge to cause the weapon to take on one of the following forms. Alternatively, you can choose to expend 2 charges to empower the chosen form.

Shield Form. A number of shards break away from the blade and form a targe-like shield on the hilt. For 1 minute, you gain a +1 bonus to your AC, but the damage die of the weapon is reduced to 1d6.
Empowered. The weapon's damage die is not reduced.

Shard Form. The 15 shards that make up the blade split apart and float in a shape that approximates a larger version of the blade. For 1 minute, the reach of this weapon is extended by 5 feet.
Empowered. The weapon's reach is extended by an additional 5 feet.

Swarm Form. The blade splits and rotates around the hilt like a swarm of angry wasps. For 1 minute, you have advantage on attacks of opportunity.
Empowered. You can use your reaction to make an attack against a creature that enters your melee range.

Launcher Form. The blade splits and all 15 shards orbit around your wrist. For 1 minute, this weapon becomes a ranged weapon with a range of 30/100 feet. Shards launched from this weapon return to orbit your wrist once the attack is finished.
Empowered. You can forgo one of your attacks to instead target a space within range. Creatures within 5 feet of this space need to make a DC 15 Dexterity saving throw, or take damage as if you had hit them with an attack with this weapon. This special attack can only be used once per round.

The Shatterblade regains both charges daily at dawn.

While in the area of an Antimagic Field, the blade loses it's cohesion, and its shards separate and drop to the ground. The blade regains its cohesion only when all 15 shards and the hilt are no longer within said area.

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

Notes: Bonus: Magic, Versatile, Sap