Five magical swords trying to do interesting things with game mechanics and allow for interesting tactics in old school games. I'll leave the specifics up to you:
A successful blow leaves a mortal wound-- even to fiends and fae-- but only five times before it rusts completely away.
Each day the blade draws no blood it becomes heavier to bear.
It never misses its mark but only leaves the tiniest mark.
Useless in battle unless next to a fast friend, in which case it will block every blow that tries to harm them.
Barbed blade, balanced oddly, bane of foe's armor.