Game Mechanics

Neverwinter Nights 2 is based on the D&D 3.5 Edition ruleset. There are a number of differences, not just related to the real-time implementation of the ruleset.

Inventory

Characters can transfer items regardless of distance and status, even while dead or in combat.

Potions

Unlike in 3.5 D&D, NWN2 potions simply cast a spell. Potions of Speed (Haste), Bless, etc. will affect creatures near the drinker as well.

Saving and Reloading

Saving and reloading causes all party members and summoned creatures to be teleported to the main character's location. This can be used to hop past small barriers, walls, and triggers. You can save and load even in combat.

Dialogue

Having a party member initiate dialog with an NPC usually teleports the group leader to that NPC.

Starting most dialogues, including forced dialogues, removes the party from combat, allowing dead party members to revive with 1 hp.

Glitches

Earlier patches have fewer features, but more glitches.

Aura Spells

If you pause the game while a creature is right at the edge of an aura (ex: Battletide, Body of the Sun, etc.), the aura sometimes reapplies itself repeatedly to that creature. Not very useful in most cases, but Body of the Sun and other damaging auras can do absurd damage this way.

Note that Body of the Sun, the most available spell to use this with, was introduced in Patch 1.01.

Infinite HP

There's an infinite HP bug if you have multiple items or effects that boost Constitution. It seems that Con-boosting items and effects check if their Con-change would cause you to gain or lose HP before they check if there are any other existing Con-modifying effects in place that they don't stack with. As such, when you put on a Con-boosting item while already under a Con-boosting effect, you get the extra HP you would have gained had the two effects stacked, and the extra HP remains even when you remove the second Con-boosting item. This can boost you well above your normal max HP. Any extra HP above maximum goes away (you just revert to your actual max HP) when you transition areas, when you rest, or when you heal any damage (for example, you can see in the log "Cure Minor Wounds heals CHARACTER for -64 hit points" if you healed while 64 hp above max). It persists through save and reload.

For example, on my level 10 character with 14 Constitution and 120 HP, I have Zachan's Amulet (+1 Con) equipped, bringing me to 15 Con. Then I equip Boots of Hardiness +1 (+1 Con). My hp increases to 130, but my max stays at 120. Because the two items don't stack, my Con stays at 15. When I remove the boots, the extra HP remains. Every time I take off and put on the boots again, I gain another 10 HP semi-permanently. Just for kicks, I got my HP up to ~1050.

This bug only works with a Con-boosting item that adds an odd numbered bonus (+1, +3, +5, etc.) so that it can add more HP when you equip it than when you remove it. You'll only get your character level in extra HP each time you unequip and equip. The earliest you can do this is Fort Locke, using the Bear's Endurance spell, Galen's Boots of Hardiness +1, and a character with an odd-numbered Con score (so it stays odd-numbered after the +4). Coincidentally, you get Elanee at Fort Locke, she can cast Bear's Endurance, and she has an odd-numbered Con score (if you don't have one yourself). If you don't want to rely on Bear's Endurance, you can snag an amulet of +2 Con from the Shadow Priest in the castle ruins, get Zachan's Amulet (+1 Con) as a quest reward from rescuing the children just outside the castle ruins, or buy an amulet of +2 Con in Neverwinter. If you rely on the spell, you have to recast it after each rest (or area transition) in order to get your HP up, which takes ~3 seconds.

On a related (but kinda useless) note, if you do it the other way around by equipping and unequipping a +1 item while you have an even-numbered Con score (after including your other Con-booster), you lose HP each time instead of gaining it. For example, having a 10 Con and Bear's Endurance, then swapping in and out Boots of Hardiness +1. On a related, but slightly useful note, even without taking it to abusive levels, you can use multiple Con-boosting spells (such as Bear's Endurance multiple times) to gain bonus HP for each casting.

This bug is present in the Steam version of the game (Patch 1.23).

The easiest way I've found to rapidly swap in and out an equipped item is just to put it in a quick slot and hit that slot repeatedly. If you use the keyboard, the game reacts for each key press. If you assign the item to multiple quickslots, you can press the keys for multiple quickslots at once to do it faster. It takes two presses (equip + remove) for each iteration, which adds 1x your level to your HP.

Infinite XP

When you get into Blacklake at the start of Chapter 2, you can go in the crypts. There's one person before the end that you can rescue with a diplomacy check. When you kill all the enemies, she'll talk to you. If you don't piss her off, she'll live and run away and give you 500 exp. But you can keep talking to her after she tries to run away and go through the dialog again. This one is accessible right after you open up Blacklake, but there would be no reason to go down to the crypts aside from it. So it's a bit out of the way. This is still present in the latest version of the game (Patch 1.23).

In chapter two, after you go through the "trial" and defeat Lorne, you can return to West Harbor to complete the quest "What Happened to Lorne" (you have to have gotten the quest in Chapter One before leaving West Harbor). Talk to Lorne's mother to complete the quest, and you'll get 500 XP. She'll say she needs to be left alone. Now talk to her again. She'll give the intro to the "quest completed" dialog, and give you 500 XP again. Rinse and repeat. (Fixed in Patch 1.01)

When in Ammon Jerro's Haven, if the player learns the true name of Zaxis he is able to command the demon to open the gate. After you open the gate you get 1000 exp. If you talk to him again you will have another option to ask him to stop referring to himself in the third person. After that option is selected the player can once again tell Zaxis to open the portal and gain another 1000 exp. This can be done for an infinite amount of times up until the party leaves Ammon Jerro's Haven. (Note: Works in 1.03)

Keep Aimee

If you skip the trigger that kills Aimee in West Harbor (for example, saving and loading to skip over the fence and then just giving Tarmas's mage battle a wide berth), Aimee won't be removed from your party. She'll be immortal for some time (unable to go under 1 HP), but this disappears after a while. What, exactly, causes the immortality to go away is unclear, but it may be related to time, damage taken, or the unsummoning of Aimee's familiar. There does not appear to be any way to remove her from the party, not even in the Sunken Flagon fight when the rest of the NPCs are removed from the party.

Polymorph Teleport

Some effects that change how much space a character takes up, like Polymorph, can cause characters to be pushed across physical boundaries like walls and doors. Polymorph teleport works similarly to Baldur's Gate, except that the character you have selected will not move (instead all other sprites get pushed away).

Unlimited Spells

While in a polymorphed form, you can cast from the quickcast menu. Not only can you cast the spells while polymorphed, but they don't appear to be spent once you cast them. So there's unlimited spells for Elanee and any mage that learns polymorph. (Confirmed in Patch 1.00, not in Patch 1.23, unconfirmed which patch fixed it.)