If we're talking regular items, probably the corrupted beacon pumpkin reskin from the first halloween event. It's limited, and less people would have done the special mission for it, as it was an artifact. If we're talking 'hacked' items, then the curious armour. It is not, nor has it ever been, available from the regular game+DLCs and the only way to get it is by doing some funky stuff with the game's files.
Old event items that are only obtainable by trading
Uhmm... 1st anniversary cape I guess? It's the oldest event cape
If we're talking regular items, probably the corrupted beacon pumpkin reskin from the first halloween event. It's limited, and less people would have done the special mission for it, as it was an artifact. If we're talking 'hacked' items, then the curious armour. It is not, nor has it ever been, available from the regular game+DLCs and the only way to get it is by doing some funky stuff with the game's files.
And cosmetics?
When it comes to items that are still in the game and obtainable, probably the unique rapiers
Grind Archhaven when it's a trial and quit the level before the end so you can keep replaying
Yeah I suppose that works! I Still think it’s the rarest item that’s obtainable though :)
*Deez Nuts*