NWN2 had a lot of feats that were just made up for the game. It's a matter of transition to video games, and their idea was very overpowering, but it still gave you a huge penalty to attack. NWN2 also didn't have a bevy of +6 items.
http://dndtools.eu/feats/complete-wa...ey-grip--1978/
That's the best link I could find on Monkey Grip, and it doesn't account for offhand.one page before, so you didn't even have to leave the threadThis is the 3.5e Monkey Grip feat (and the 2005 errata of Complete Warrior doesn't change the 2003 edition one), it doesn't allow 2handed weapons to be used in one hand, much less the use of double weapons in one hand or 2h weapons to be used in an off hand.Originally Posted by Complete Warrior,p. 103,WotC 2003
Monkey grip [general]
You are able to use a larger weapon than other people your size
Prerequisite:Base attack bonus +1.
Benefit: You can use melee weapons one size category larger than you are with a -2 penalty on the attack roll, but the amount of effort it takes you to use the weapon does not change. For instance, a Large longsword (a one-handed weapon for a large Large creature) is considered a two-handed weapon for a Medium creature that does not have this feat. For a Medium creature that has this feat, it is still considered a one-handed weapon. You can wield a larger light weapon as a light weapon, or a larger two-handed weapon in two hands. You cannot wield a larger weapon in your off hand, and you cannot use this feat with a double weapon.
Normal: You can use a melee weapon one size category larger than you are with a -2 penalty on the attack roll, and the amount of effort it takes to use the weapon increases. A larger light weapon is considered a one-handed weapon, a larger one-handed weapon is considered a two-handed weapon, and you cannot use a two-handed weapon at all.
Now some DM:s allowed for 2h weapons to be wielded in one hand based on the weapon size conversion table, which is fine but just like the above webpage quote is a home brewed house ruling of the feat. Why was this something many discussed and house ruled, well likely because in 3.0 it was allowed and the feat was pretty bad otherwise and almost always worse than Power attack.