I've been recently running around with a character which uses Trident as his main weapon so figured I would share what I have found out through testing about it. The NWN wiki is a little bit unclear what works and what not for Tridents so here You go:
Trident (Arelith version)
Feats working with Trident:Base Damage: 2d6
Base crit: 20/x3
Damage Type: Piercing
Weapon type: Martial
Weapon size: Large
Weight: 5 lbs
Feats NOT working with Trident:Weapon Specialization, Epic Weapon Specialization, Epic Weapon Focus, Overwhelming Critical, All of the WMs feats, Bane of Enemies.
Strength modifier:Weapon Focus (though still counts for WS and EWF requirements)
Arelith Special:+1 damage/st mod when using One handed (Large PCs)
+1.5 damage/st mod when using Two Handed (Medium PCs)
Average damage:+2 AB (as a two handed weapon)
Compatible with the "-twohand" command, properly boosts both AB (+2 AB) and Damage (additional +0.5 per ST mod point) for Large-sized PCs.
Descriptive comparison:7 (Greatsword equivalent)
Best comparison for Tridents is a Greatsword due to its exact average damage value. The Greatsword will reflect marginally better performance at lower AC values (where confirming crits will be easier), while Trident will perform better at high AC values when crit confirmation will be possible only at rolls of 20s.
For a WM weapon Trident will perform slightly worse in overall then a a Greatsword but will present a more "bursty" character of damage with expected crits around 200 damage point mark (depends on the strength and buffs).
The Piercing-damage type of the Trident makes it more suitable to use against enemies that do not use Shields as Slashing damage immunity in Arelith is usually located on the Armor of an enemy.
Final remarks:
Generally a very good weapon in overall, marginally worse then a Greatsword but superior to most of other Two-handed weapons.
Q&A:
Q1: Can You stab a goblin/gnome/hin on it and wave it in air?
A: Yes You can! (disclaimer: Visual not supported)
Q2: Can You poke a dragon with it like a mosquito?
A: Yes You can! (disclaimer: "poking" dragons with sharp sticks not advised)
Q3: Can You RP using it as a barbeque skewer over a fireplace?
A: Yes You can! (Q1 and Q3 highly advised for RP-shenanigans)
Q4: Can it pierce Stoneskin/Premonition?
A: With a GMW scroll or Fighter lvl 25 it can.
Q5: Can it be disarmed?
A: Yes, though chances for a successful disarm against a Large-sized weapon are slim.