Improved trip

From DDO wiki

Improved trip has a chance to trip the target, rendering it prone for a longer period of time than Trip. It has a cooldown of 10 seconds. This feat replaces Trip as an action.

In game description: Using this attack, you may trip the target, rendering it prone for a longer time. Some creatures may be immune to this effect.

Game Mechanic is as follows:

• A attack roll is made against the target. Like any melee special attack, it works with your combat flow and is queued to work on your next melee attack. Ideally you will time this so that it will work at your maximum attack bonus.
• If it hits, it will do normal damage, and in addition attempt to trip the target.
• The target then takes a Strength or Dexterity check (whichever is higher) against a DC of 14 + Strength modifier + related Enhancements + Vertigo weapon. Should the target fail its check, the target is tripped.
• The target remains tripped for up to 60 seconds, during which time it is rendered prone and may not move or attack. Prone targets suffer -4 AC. Attacks/spells already started will complete, however.
• Prone creatures are given a Balance skill check every 2 seconds to stand up early. The DC on it is the same as the trip DC, but it uses the Balance skill rather then Strength or Dexterity.

Some creatures are immune to tripping, such as those that have no legs (like oozes) and those that naturally hover or levitate (such as mephits and ghosts). Red and purple named creatures are also immune.

As of Module 5, your character's size doesn't effect your chance to trip. Mostly this means Halflings do not suffer -4 to their trip attempts for being small. However larger monsters, or monsters with many legs, are given appropriate bonuses to resist the trip, +4 per size difference or +8 or greater for creatures with many legs.

Prerequisite: Combat Expertise

A fighter may select this as one of his fighter bonus feats.