Lethargic Assail

Barbarians can now apply a special On Hit Property called Lethargic Assail using their Crafting Menu for a cost of 500 gold coins.

The duration is 1 Turn per Barbarian Level.

To apply this On Hit Property the Character must meet the prereqs:

Mighty Rage-Feat
Melee Weapon Equipped.
26 Barbarian Levels.

Once the On Hit Property is applied to a Melee Weapon, the following will happen if the character succesfully lands a hit on someone and all the below criterias have been met.

Criterias:

16-20 must be rolled on a 20 dice.

Saves:

Now the Target makes a Will Save.
The check is:
DC: 13 + Barbarian Levels.

If the Target fails the save, they become frozen (immobilized) for two seconds and slowed for 0.5 seconds per barbarian level.
If the Target rolls a 20 it's a Auto Resist and the Target will not be frozen.
If the Target rolls a 1 it's a Auto Failure and the Target will get a frozen.

Since it's an On Hit Property it requires the Barbarian to hit her Target for the effect to even being checking, so Concealment and AC will help you avoid getting frozen or slowed.

Note that a Frozen (Immobilized) target can still preform any action, except moving.

Also note that Spell Craft or other Spell-oriented bonuses to Saves will not help against the DC check of Lethargic Assail.