A masterfuly crafted bow from an undeterminable type of wood. Runes made from different metals promise the demise of ones enemies. They seem to sense which language the creature holding is able to read and change shape to represent it's glyphs.
The bow appears to be a smaller than normal shortbow but a creature holding it, wether it is attuned to it or not senses the ability of the bow to grow and shrink, and can command it to do so with only a thought.
In it's bigger form it takes the shape of a greatbow standing about 8ft tall and a quiver manifests holding an endless amount of arrows of the appropriate size.

The Bow is only able to shoot in its greatbow form and only with the arrows from the manifested quiver.  The creature holding it can grow or shrink the bow as a free action or part as a movement. It is unusable by creatures of smaller than medium size. It is uneffected by effects that cancle magical effects. It's attacks count as magic attacks. You get a +1 bonus to attack and damage rolls using this weapon. It's damage die is a d10.

Whenever you make an attack roll with this weapon, befor you roll the d20, you have to roll 1d12 to determine an additional effect from the table below.
If specified you don't have to roll the d20 to hit after learning the effect from the d12. If nothing is specified make a normal attack roll.

---

1. The tip of the arrow ignites in fire.
   -> If the attack hits, deal 1d8 extra fire damage to the creature.
   -> If the attack misses the bow heats up to a glowing orange and burns you for 1d6 fire damage
   
   
2. After the arrow leaves the string, the bow begins to pull the ground up and encases itself and you in hardened rock and dirt.
   -> Until the start of your next turn you get a +5 to your AC and auto succed on any dex-saves to halven damage.
   -> Also your speed drops to 0ft.
   -> Has no effect if you are not touching the ground. If you're touching water until the start of your next turn you get encased in a water bubble and start to suffocate and your turn ends immediatly.
   
   
3. The bow starts to crackle with electrical energy which springs over to you.
   -> You gain +10ft Movement speed until the start of your next turn.
   -> This turn you have to move at least 10ft in any direction, if you're unable to move you take 1d8 lightning damage.
   
   
4. A strong wind picks up your arrow.
   -> You don't roll to hit, your arrow hits every creature in a 120ft straight line from you to your target and beyond.
   -> For the next 3 turns you have disadvantage on all your ranged attacks, as strong winds carry your arrows adrift.
   
   
5. Your arrow alights with bright green energy and flowers begin to sprout along its shaft.
   -> If the attack hits, the creature heals for 1d6 hit points. You also heal for the same amount +3.
   -> If the attack misses you take 1d4 necrotic damage, as your lifeforce nourishes the sprout of flowers along the limbs of the bow.
   
   
6. Time seems to slow around you.
   -> You don't roll to hit, you have all the time to aim and perfectly align your shot with the targeted creature, you deal an extra 1d12 piercing damage.
   -> You are suffering the effects of the slow-spell until the end of your next turn.
   
   
7. The tip of your arrow reshapes itself to look like a stylized heart.
   -> You don't roll to hit, your arrow seeks out the targeted creature and hits it. Until the end of it's next turn, the creature falls madly in love with you and does everything to protect you and kill all your enemies.
   -> You also fall madly in love with the targeted creature until the end of your next turn and do everything to protect it and kill all it's enemies.
   
   
8. The arrow becomes flesh and grows a mulitude of mouth that begin to scream which only you can hear.
   -> If you hit the creature you deal an extra 1d10 psychic damage as the screams wreak havoc in it's mind.
   -> The creatures mind ignites in painful rage at your existance, it can move up to double it's movement speed towards you, not provoking attacks of opportunity and can make a single attack towards you, if you are in range for a meele or ranged attack, supposed the creature has an attack action of sorts.
   
   
9. No notable effect manifests.
   -> You make a normal d20 attack roll adding all applicable modifiers and dealing your standard damage.
   
   
10. The arrow draws a rainbow pattern where it flies.
    -> From you in a 30ft. cone which direction is centered on the target, all creatures and objects suffer the effects from the Faerie Fire-Spell until the start of your next turn.
    -> You also suffers from the effects.
    
    
11. The tip of the arrow reshapes to form a jar containing a dark liquid.
    -> On a hit the arrow deals no damage and in a 15ft sphere centered on the targeted creature the ground is covered in a sticky substance making it difficult terrain.
    -> On a miss the bow secretes an oily substance and the creature holding it loses its grip and must use an action to take up the bow again.
    
    
12. The air around you cools down to freezing temperatures.
    -> For the next 3 turns at the start of your turn you gain the effects of the Armor of Agathys-spell at 3th-Level.
    -> Also your weapon die is reduced from a d10 to a d6 until the effect ends.
    -> Until the end of the 3rd turn, if the number on the d12 to determine the additional effect isn't a 1 or a 12, ignore the effect. A 1 on the d12 ends the effect prematurely ending the Armor of Agathys-spell. A 12 starts the effect anew.

---

Curse
The bow is cursed and only reveals the negative effects after a creature attunes to it.
An attuned creature can not release it's attunement or attune to another item with this slot until the curse is lifted for example by a greater restoration spell.
The curse also affects the ability to use other weapons, until the curse is lifted an attuned creature is unable to use any other weapon to make an attack.
In meele the Bow reverts to it's smaller form growing a knuckle ring to cover the users fist. The bow deals 1d4+str bludgeoning damage, you also take half of the dealt damage. Do not use your proficency bonus for your to hit roll on a meele attack.

---

 

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

Notes: Bonus: Magic, Ranged Weapon Attack: Piercing, A creature with proficency in longbows. It takes one hour of meditation, touching the bow to attune to it., Damage, Combat, Ammunition, Heavy, Range, Two-Handed, Slow