The idea is really simple, you run a dungeon and at the end of it is a chest which "MAY" contain a blueprint with x number of crafts available, this blueprint would be for a known item but with 1 or more additional random stats.
For example you might run a dungeon, or kill moder and have them drop a 1 run Fine Bow blueprint which adds an additional +10 fire damage, or maybe you drop a 1 run blueprint for a Silver Shield that has an Attacker takes x damage stat on it.
I hate rng in crafting but if its in the blue print then the player knows exactly what he's going to get when he crafts the thing, this would open up lots of trade between players who find and or craft cool stuff, the more options available for this system the better it would be.
Some suggestions off the top of my head would be.
Attacker takes Damage
Heal for % of damage taken
Randomly teleport on damage received.
Deflect ranged attacks back at attacker for half damage
Critical Strikes summon a nearby wolf to aid you for a short time
Doom , Deals 50% more base damage, but has a 5% chance to kill you.
just some rough ideas lol.