Just opening this up, don't care about winning care about sharing. Here is mine:
Silverrain +1 Longbow of Quenching
Silverrain was created shortly after the Cataclysm as a rare collaboration between the dilynwyr henfyrd and the Sitherna. With the introduction of the humans and the orcs and the use of the forest for industry the elves created a protector of the forest and that protector is Silverrain. It extinguishes all fires in its 30ft cube centered on a point within range. The spell can dispel magical fires or fire spells. To do so, make an Intelligence (Arcana) skill check (DC equals 10 + the spell's level). On success, the fires within the area are dispelled. If there is a Fire Elemental or a creature with the fire subtype, targets within the area takes 8d6 cold damage.
Silverrain is a 6' tall bow with a motif of elves in a forest raining down a hail of arrows on humanoid forest encroachers with axe and flame. A carved depiction of a vine winds its way up the bow from the top to the bottom. When an arrow is knocked the magical properties of the bow cause the appearance of swirling water to appear in the arrowhead of the knocked arrow.
I like this idea!
I submitted a spear, called Amelie's Refusal. It deals +1 damage (piercing or slashing) with a +3 to-hit (bonuses which are doubled during Opportunity Attacks), and grants the wielder advantage on Death Saving Throws. It does require attunement.
I wanted to create a magical weapon that could be useful to a wide variety of characters. Spears are Simple weapons, have the Versatile trait, and can be thrown, which makes them usable by a wide number of classes in a wide variety of circumstances, regardless of whether or not you take feats to specialize in them.
The shaft is of average length (around 6'ft), topped with a thick, longer-than-average blade that can cut as well as stab (hence the piercing or slashing damage). The shaft is a dark, unadorned maple, and the unblemished blade is covered in acid-etched runes. A handful of purple and orange tassles are affixed to the spear where the shaft meets the blade.
The +1 damage and +3 to-hit puts the focus on consistent, low-moderate damage output, allowing non-martial classes (and even those without proficiency) some degree of efficacy at low levels. Doubling these bonuses during Opportunity Attacks makes Amelie's Refusal a viable option for higher level or more martial classes which focus on exploiting OA's.
Advantage on Death Saving Throws makes it an intriguing option for any squishy/damage-prone character, or one that has a tendency to separate from the group for flanking manoeuvres.
More than making a versatile weapon that has some kind of value (however small) from the earliest to the latest parts of the game, I wanted to create a weapon that is magic because of its experiences, rather than because it was intentionally crafted. So I wrote some backstory (and a ballad) about it's first owner and what she did with it, to explain the enchantments that it has. (I'll link to the Google Doc I used if anyone wants to read it)
https://docs.google.com/document/d/1459uzJRolBQc2Eg7lq9c-TzYD0ifphI7jLC3aUjIugo/edit?usp=sharing
I'm having a lot of fun writing for these design contests, and reading everyone's entries. Here's hoping this isn't the last.