The benefit of the feat Owlbear Berserker says
When grappling, you can make an unarmed attack to deal 1d6 points of normal damage with a successful grapple check. You do not suffer the usual −4 penalty for dealing normal damage. (Unapproachable East 44)
What does this feat's benefit allow a creature to do?
Here are some readings.
- The benefit only increase the creature's damage dealt (and eliminates the creature's penalty) when the creature takes the action Damage Your Opponent. That is, the benefit, essentially, improves the creature's (presumably lousy) unarmed strike damage.
- Each time the creature makes a successful grapple check, it can make an unarmed strike (at a −4 penalty) that deals 1d6 points of damage (as per Attack Your Opponent).
- While grappling, once per attack (or, alternatively, as a standard action) the creature can make a grapple check; success means the creature can take a free action to make an unarmed strike that deals 1d6 points of damage. Note: The least likely reading, but nonetheless possibly useful if the creature also has the extraordinary ability constrict.
The feat is unmentioned by the D&D Frequently Asked Questions, and Unapproachable East's errata has one entry (it's not for this feat). The feat is rarely mentioned: for example, here as an unattractive feat for a barbarian and in this Project Gutenberg collection of owlbear ephemera. The feat doesn't seem to have received further analysis. As an official ruling is unlikely to come to light, careful textual analysis is preferred over house rules and speculation.