The Abyss and the Nine Hells would never be the same when a creature of impossible power crossed the multiverses and began slaughtering their denizens left and right. When the gods finally managed to banish the creature to its rightful realm, it left behind its weapon. A thing of awesome but brutal and unknowable power, it was better left sealed away. 

The Slayer's Relic is considered a unique firearm. It is two-handed, weighs 15 lbs, has a range of 30 feet with no long range band, and it deals 2d10 piercing damage. It does not misfire and it does not need to be manually reloaded. 

Dormant

The Slayer's Relic grants the following benefits in its dormant state: 

• You gain a +1 to attack and damage rolls made with this magic weapon. 
• The relic has six (6) pieces of unique ammo and cannot be loaded with another kind. It automatically refills its own ammo on a short or long rest. 
• If you kill an enemy creature with this relic, it regains two (2) pieces of ammo. 
• The Slayer's Relic does not suffer disadvantage on ranged attack rolls against targets within melee range of you. Such targets suffer a critical hit from the relic on a natural roll of 18-20. 

Awakened

When the Slayer's Relic reaches the awakened state, it gains the following properties: 

• ???

Exalted

When the Slayer's Relic reaches the exalted state, it gains the following properties: 

• ???

It’s up to you to decide whether a character has proficiency with a firearm. Characters in most D&D worlds wouldn’t have such proficiency. During their downtime, characters can use the training rules in the Player’s Handbook to acquire proficiency, assuming that they have enough ammunition to keep the weapons working while mastering their use.

Notes: Range, Two-Handed, Ammunition (Firearms), Reload, Push