Castle Whiterock: The Duergar, part 2

The second part of the exercise, understanding how duergar fight is the more difficult aspect, at least to me.

I tend to get muddled in combat, as a DM. I'm constantly forgetting special attacks my monsters have, their tactical tricks forgotten in the fog of war as I'm bombarded with questions. But for these fights it will be extremely important to understand how they should be played.

First off, they have the usual dwarven abilities; resistant to magic and stable. So they are slow but sturdy, getting +2 on their saves against magic and +4 on their CMD against bull rush attempts or the dreaded (and IMHO overpowered) trip attack. 

On top of that, they see in the dark. With 120-foot darkvision, they will see you coming in pitch darkness, probably before you are even aware of them. 

Likewise, they are immune to paralysis, poison and phantasms, meaning they can drop area of effect attacks with relative impunity, if they need to exert some crowd control. 

Lastly, and perhaps most especially, they have two spell-like abilities; invisibility and enlarge person (self), both once per day. While only useful once per day, they are real game changers, essentially giving them control over how fights begin or end. Let's review. 

Invisibility

Perhaps the most overused and misunderstood spell of them all. Within the game, invisibility lasts a minute per level (based on the duergar's class level, in this case) and allows the target broad leeway in their actions so long as they don't directly attack. From the SRD: 

"Thus, an invisible being can open doors, talk, eat, climb stairs, summon monsters and have them attack, cut the ropes holding a rope bridge while enemies are on the bridge, remotely trigger traps, open a portcullis to release attack dogs, and so forth."

That's a lot of shenanigans you can get into while invisible. But it is far from all of what this spell gives you! Elsewhere in the SRD, it also gives you a +40 (if immobile) or +20 (if moving) bonus to your Stealth checks, good enough to override the massive Stealth penalties of heavy armor, and grants you a +2 non-typed bonus to hit another creature and ignore their dexterity bonus to armor class while invisible. While that ends your invisibility, it can be a game-changer, especially if the duergar in question possesses sneak attack capability. 

So you can choose to either begin combat invisible and get the drop on a foe, or save your invisibility for later to escape combat. Nice!

Enlarge Person

This one actually requires a little more of you, mechanically. It seems like doubling your height and octupling (if that's a word) your weight would increase your strength by more than +2, but the benefits still outweigh the drawbacks. The aforementioned Strength bonus, coupled with reach, outweigh the penalty to Dex and armor class. Your net delta is +0 to attacks, +1 damage, -2 to AC and -1 to Reflex saves, but your reach increases to 10 feet and your damage increment is upgraded due to size. In addition, your increased size gives you a +1 bonus on your CMB and CMD, which will be beneficial to the Stalwart Defender. 

I can see both these abilities playing out differently depending on the purpose of the encounter. 

A) Feeling out the abilities of the enemy - using invisibility to disengage from the fight.
B) Setting up a lethal ambush - an alpha strike in which invisibility and enlarge person are used in combination to control the first round of combat, hitting as hard as possible in order to capture or kill the opponent, or at the very least, prevent them from pursuing as the duergar escape.
C) Performing a holding action - using enlarge person to lock the enemy in place while the rest of the group falls back to a better position or escapes.