One of my players found a magical rapier on my random room search table last session.
The magical effect I rolled was red colour trails that follow the blade.
Neat! But in keeping with the LotFP ethos of magic items being powerful, unknowable, and potentially self destructive, here's the Red Rapier as I'll be using it in my game.
Leather-wrapped hilt, blade of folded steel.
If identified, its name is Thirst.
It drinks blood, and so its blade is always clean.
It gains power as it consumes blood.
Killing a living creature with it embeds the rapier in the creature for one round as it guzzles on the juices. Intelligent creatures add 3 charges, non-intelligent creatures add 1 charge.
Nonliving or bloodless creatures do not add charges.
At midnight every night it loses 3 charges, or resets completely if it has tasted no blood that day.
0 Ordinary rapier
1 Leaves a trail of red afterimages.
2-3 No penalty to hit against high AC
4-6 Hilt becomes sticky and damp, leaves red residue on hand.
7-9 Somehow sits better in wielder's hand, +1 to hit.
10-12 Glows a deep red in dim light. Bearer is subtly encouraged by DM to kill things. "He surrenders, but you see a crazy gleam in his eyes like he'll kill you as soon as your back is turned." etc.
13-15 Seeks arteries, +2 to hit and +1 to damage. Bearers hands are bloody when they leave the sword, and a bloody spot on the bearer's palm cannot be washed off. Out damn spot!
16-18 Blade seems like translucent frosted glass filled with a viscous red liquid. "Accidentally" kills people held at rapierpoint, fighting in friendly duels, etc. Crits on 19-20.
19-21 Bearer's palms and fingertips turn a deep umber. Can sacrifice hit points to gain that much + to crit range. Declare before rolling.
22-24 Blade looks like clear glass filled with viscous red liquid. Bearer's arms are red like sunburn. Missing an attack drains 1d4 HP from user, but allows a reroll. Critical hits heal 1d8 HP (even above maximum).
25-27 Blood beads from the blade. If given opportunity to spare a life, the bearer is filled with bloodlust. Bearer's eyes are bestial, yellow and slitted. +2 to hit, +2 to damage.
28-30 Blood gloops along blade like this. Skin is deep scarlet, nails are cruel claws, teeth are fangs. While the blade guzzles on blood, you get a flash of insight into the person they were. "Argued with his wife this morning", "dog's fondest memory is staring up at his mother as a puppy", etc. +3 to hit, +3 to damage.
31+ Blade becomes a long clear blade of crimson crystal. They know that if the blade goes a day without tasting blood and resets, the bearer dies and their body dessicates as their soul is consumed. Otherwise, the bearer cannot be killed by any means.
The bearer must Save vs Magical Device (Wis mod applies) every time they drain blood, else go wild with bloodlust and attempt to kill every living thing in the area.