Rapier of the Black Tentacle (Patreon)

Weapon (rapier), rare

This dark silver rapier sounds weighty as it whips through the air. You gain a +1 bonus to attack and damage rolls made with this magic weapon. When underwater, the weapon gains the reach property (elongating elastically when swung), and you don't have disadvantage on attack rolls with it as a result of underwater combat.

While holding the rapier, you can use an action to cast the black tentacles spell from it (save DC 15). This version of the spell doesn't require concentration; it fills a 20-foot cone, originating from you, instead of its normal area and range, and ends at the end of your next turn. Once this property of the rapier has been used, it can't be used again until the next dawn.

I'm sure I died that night. I sank like a stone, I did. I remember the darkness dragging me down. But...maybe it was something else—something sinister. Maybe it were just a bad dream, fueled by one-too-many djinn and tonics.

You might have been able to convince me of that if it weren't for this damned sword. What in the Three Tides did I get myself into now.