Set Items and Unique Items sometimes have special magical effects that are not found on any Magic or Rare item. This is not a complete listing of all special effects.

Deadly Strike
This is a chance of doing double damage. This bonus is applied after skills such as Critical Strike and any other damage bonuses. Critical Strike (CS) and Deadly Strike (DS) exclude each other.

If you have a 33% Deadly Strike item, and 68% Critical Strike Skill the complete chance to get double damage is:

=CS + (DS/100)*(100-CS)
=68% + (33/100)*32%
=68% + 10.56%
=78.56%

It is possible to get up to 100% chance for Deadly Strike. Anything above 100% is discarded.

Open Wounds
This is a chance of making a monster bleed uncontrollably. They lose health while bleeding. Open Wounds Items stack in most cases.

Duration: 200 frames (that is 8 seconds).

The damage per frame seems to be the following (where Clvl is the attackers level, that is the player's level usually):

Clvl=1-15: (9*Clvl+31)/256
Clvl=16-30: (18*Clvl-104)/256
Clvl=31-45: (27*Clvl-374)/256
Clvl=46-60: (36*Clvl-779)/256
Clvl=61-99: (45*Clvl-1319)/256

If you prefer per second, just multiply by 25:

Clvl=1-15: 25*(9*Clvl+31)/256
Clvl=16-30: 25*(18*Clvl-104)/256
Clvl=31-45: 25*(27*Clvl-374)/256
Clvl=46-60: 25*(36*Clvl-779)/256
Clvl=61-99: 25*(45*Clvl-1319)/256

Some examples:

Clvl 10: 11.8 per sec over 8 seconds for a total of 94.5 damage. Clvl 30: 42.6 per sec over 8 seconds for a total of 340.6 damage. Clvl 50: 99.7 per sec over 8 seconds for a total of 797.7 damage. Clvl 70: 178.8 per sec over 8 seconds for a total of 1430.5 damage. Clvl 90: 266.7 per sec over 8 seconds for a total of 2133.6 damage.

Also, the damage is divided by 4 for a player target. In addition, for a missile versus a player target one should divide the damage by 8 instead.

Finally, versus bosses and champions (could be just bosses or special bosses) the damage is divided by 2.

It is possible to get up to 100% chance for Open Wounds. Anything above 100% is discarded.

Crushing Blow
This is a chance of reducing a monster's health by X% in a single blow.

-Default: 1/4th
-vs. Players: 1/10th
-vs. Hirelings: 1/10th
-vs. Champions, Uniques, Bosses: 1/8th
-with missile weapons, default: 1/8th
-with missile weapons, vs. Players: 1/20th
-with missile weapons, vs Hirelings: 1/20th
-with missile weapons, vs Champions, Uniques, Bosses: 1/16th

The life removed is also scaled with number of players. So that if a monster has 450% more life due to 8 players (or whatever the value is) the life removed is further reduced by the same amount (450% would equal multiplying by 4.5 so the life removed by Crushing Blow is divided by 4.5).

• It is possible to get up to 100% chance for Crushing Blow. Anything above 100% is discarded.
• Physical resistance does apply to Crushing Blow damage, but only if the resistance is positive.
• Crushing Blow Items stack in most cases.
• Since 1.10 Crushing Blow is calculated before your normal damage. So, before doing the damage that you would normally do, there is a chance you will reduce the health of the monster by X% then normal damage apply to the resulting lower life. If you have more than one item with Crushing Blow, the probabilities will be added together. There will be one random check for a Crushing Blow. There is no check for each separate item, so one can not get multiple Crushing Blows in one attack.

Hit Causes Monster to Flee
This is very similar to the Barbarian Howl Warcry and is also similar to Howling items.

Defense vs Missile
Reduces the % chance of getting hit by missiles (by raising the effective armor rating).

Hit Freezes Target
This bonus is pretty obvious. Items with Hit Freezes Target has a chance to Freeze Targets. Formulae:

The chance of freezing is 50 + (AL + (B*4) - DL) * 5

AL = attacker level
DL = defender level
B = freeze bonus from item (default is 1)

if it's ranged, the AL has a -6 penalty.
if it's ranged, the chance is divided by 3

freeze length = (chance - roll) * 2 + 25 frames
with a minimum length of 25 frames (1 second) and a maximum length of 250 frames (10 seconds)

Hit Blinds Target
Decreases radius of awareness similar to the Necromancer Curse: Dim Vision.

The formula is as follows:

Chance = 50 + (Attacker Level + (Bonus * 4) - Defender Level) * 5

Where the bonus is how many items of hit blinds target the character has -1. Some items have something like hit blinds target +2, which means they count as 2 items for the bonus calculation. Missile Attacks are at 1/3 this chance.

The level of Dim Vision that's cast on the target is equal to (Chance - Roll)/5+1, max of 20.

Slows Target By %
This appears to be a blue Cold Damage attack but is not actually a cold attack.

This ability is limited to no more than 50% slowing in PvP.

Ignores Target Defense (Armor Class)
This ability will not work on Unique Monsters, Super Unique Monsters, Hirelings, other players, and Act-end bosses.

What the game does is that set the Defensive Rating of the target to 0. That means it simplifies to:

AR = 100 * 2 * alvl / (alvl + dlvl)

AR = Attack Rating; alvl = Level of Attacker; dlvl = Level of Defender.

So there is still an effect of the level difference on the chance to hit and there is still a minimum of 5% and a maximum of 95% chance to hit.

Absorption (Or Absorbs)
Absorb heals the player - which is equivalent to resistance. If you have 5% Absorb Fire, 5% of the Fire that would hurt heals you instead - roughly equivalent to 10% Resistance. It is not bound by the resistance cap however.

+ Fire Skills
+ Fire Skills include all of the Sorceress Fire Tree, Amazon (Fire Arrow, Explosive Arrow, Immolation Arrow), Paladin (Holy Fire), Druid (Fire Claws, Firestorm, Molten Boulder, Fissure, Volcano, Armageddon), Assassin (Fists of Fire, Fire Blast, Wake of Fire, Wake of Inferno) and Necromancer (Fire Golem, Corpse Explosion).

On Striking
On Striking means if you actually hit a Monster.

On Attack
On Attack means every time you swing.

When Struck
When your character is hit.