I was thinking more of something along the lines of: if a weapon is "prepared in this" (like sharpened if it's a sharpening wheel) its first critical hit that day deals an extra die of damage, then loses its especially sharp edge.
I don't really know, didn't give it too much thought yet. Maybe "you can make a magical rope form between the bow and the last arrow you shot". That ought to cause some chaos.
The barb's spear:>I'm using generic names here just because I haven't really thought them up yet
Also worthy of notice that magic weapons don't get +1, +2 or +3 in this scenario, in general.
(Pike, requires attunement)
Looks like greenish bronze that was found underwater. Has holes in its tip which hold liquids like a pen with ink.
The wielder never has to make any checks due to being on a wet surface (such as an acrobatics check not to fall).
Whenever this weapon is wet, it deals 1 extra point of damage.
If the wielder has a proficiency bonus of at least +4
The damage increases to 1d6.
If the wielder has the polearm master feat
Whenever you hit with the Attack of Oportunity from someone entering your reach, you may move the creature 5ft to the left or to the right, as long as it’s medium or smaller
If the wielder has the great weapon master feat
Whenever you take the -5 penalty on your attack roll, if that attack hits, you may cause the opponent to bleed out. This effect works like a bearded devil’s glaive.
If the McGuffin is placed on its shaft
The weapon now lets you cast the following spells (DC 15):
Tidal Wave 1/day
Control Water 1/week
Tsunami - once. This can be recharged by a caster (who can use this spell) spending an 8th level or higher spell slot for five consecutive days.
If the wielder drowns
Afterwards, the wielder can cast Water Breathing as a ritual as long as he’s attuned.