Here is a list of the special weapons that you can find in the chests that enemies drop sometimes.
Coop Special Item Descriptions
Javelin bow.
A bow that fires javelins
Knockdown mace.
Knocks down everyone it hits.
Blood drain throwing knives.
Restore health to the thrower, with successful hits.
Doom javelins.
Gradually deplete the health of those they impale. Depletes 5% per second for 10 seconds.
Disarming throwing axe.
Disarms on impact. If it hits, the opponent will drop a weapon or shield.
Instakill knife.
Kills with even the slightest touch.
Backstabber.
Kills any foe with a stab from behind.
Weak berserker dart.
Depletes health but provokes a dangerous frenzy, makes you run 50% faster and hit twice as hard.
Team change dart.
Causes the person it strikes to change their allegiance. With this you can collect a small army. You can also use it to capture the King in the final wave to get more waves if you want to.
Awesome spear.
This spear is awesome with much higher speed and damage.
Running boots.
Makes you run 50% faster then normal.
Power gloves.
Makes you hit harder. These gloves gives you a 50% attack bonus with any melee weapon.
Invulnerable helmet.
Keeps your head safer, best helmet with 63 in head armor.
Kicking boots.
Deliver a nasty kick.
Restore health armour.
Restores health gradually. Heals 5% per second.