It is most likely a mount, and I think it is sleigh.
Back then, I was all over the field (Everyone spammed sleigh)
But then came more, and I was useless to wield (Better mounts such as ducky came out)
One year later came another like me (Plane was added, the other flying mount)
Attained, unlike from I, by a key (This is the one I am the least confident on but Frost JR dropped a key when he died)
If I said my name, would you even bat an eye? (The last 2 lines are just about how no one uses it now)
Maybe, maybe not, but soon I will try (^)
Hint 1: it's an item (Mounts are considered items)
Hint 2: It doesn't appear in your inventory (Mounts do not appear in your inventory)
Hint 3: The first of its kind didn't exist until late 2017. (That was when mounts were added)
So my guess is Sleigh, if that is wrong I am 90% certain that it is a mount.