How does disarming a monster affect its statistics?

The disarm maneuver has almost totally disappeared from D&D 4th edition. However, at least one Fighter power - Exorcism of Steel - allows it.

Exorcism of Steel - Fighter Attack 17
You make a powerful chopping attack against your foe, forcing it to drop what it is holding.
Encounter * Martial, Weapon
Standard Action - Melee weapon
Target: One creature
Attack: Strength vs. Reflex
Hit: 2[W] + Strength modifier damage, and the target drops one item it is holding. You can choose to catch the item in a free hand or have it land in your space.

Now...

1. I know that some monster powers explicitly require the use of an item because they state so in their power description (like the Drow BlademasterDDI Excruciating Stab).
2. I also have no problem in judging that a monster power whose name matches one of the items in its possession requires that item in order to be activated (like the Goblin CutterDDI Short Sword).

However, 2 questions arise.

What if a power doesn't match neither of two categories above?

For example: the Lolthbound GoblinDDI Stinging Blow

Stinging Blow (standard, encounter) * Poison, Weapon
+10 vs AC; 1d8+5 poison damage (crit 1d8 + 13), and if the target is taking ongoing poison damage, that ongoing damage increases by 5.

Is the Goblin able to use that power if the Fighter has deprived him of his war pick?

Is there a general (quick) rule for judging the lack of precision and damage potential a disarm maneuver (like Exorcism of Steel) should produce? The first that comes to my mind is to give the monster a -2 penalty to attacks with weapon/item-sensitive powers and to make them deal half damage.
Should the Dungeon Master instead reverse engineer the proficiency, special quality and intrinsic magic bonus of a weapon (or implement) of a level appropriate for the creature?

Final note: I know that this is the appropriate field where a DM should step in and take decisions. I'm only wondering if Exorcism of Steel is a true exception in the D&D 4th framework or if it has some sort of rule support.

Fundamentally, this is a relic of MM1 monster design. Monsters in MM1 followed the naturalistic 3.5 style "they should have damage equal to their equipment." Creating the absolutely worthless Orc Beserker with a boring power called "Greataxe" that completely ignores the damage requirements (introduced in MM3) of its level and tends to splatter low-level parties on crits.

Furthermore, the discussion on wizards site seems to have everyone just as puzzled as we are. Here is one non-worthless thread. In summary:

As far as what actions a disarmed monster could take, I'd say that in general, the creature can no longer use powers with the weapon keyword. They can use a basic attack, using the number next to their Strength score, and dealing 1d4+Str modifier damage. Use common sense, though: a marilith with six scimitars is unlikely to be seriously affected by losing one.

Thus, exorcism of steel is a "Trap" power for both sides of the table. On the players' side, less than half of the monsters in that range have a "weapon" keyworded power. On the GM's side, this power if it hits, can completely nerf a solo or elite for an entire combat.

From a practical matter, treat an "unarmed" creature making weapon keyworded attacks as -2 to attack and -2 to damage until they recover their weapon. The damage decrement is a little low, but monsters have stopped following weapon guidelines. The -2 to attack represents the average proficiency of the weapon (not at all accounted for in monster stats, but hey..)

In general, discourage your players from taking this power as it won't prove a fun experience for anyone.

• Instead of -2 to damage, try "any max damage die is treated as a 1". It scales better with monster level than -2, and it can be fun if you show the players the damage roll (they get to see a bunch of damage removed).
– Yakk
Aug 1 '14 at 20:13

Weapon

An accessory type. This keyword identifies a power that is used with a weapon, which can be an unarmed strike.

Since the power has the weapon keyword, it requires a weapon to use. In your example, since the Goblin is not wielding his war pick, he must either spend an action to retrieve it or attack unarmed.

Unarmed

When you punch, kick, elbow, knee, or even head butt an opponent, you’re making an unarmed strike. A simple unarmed attack is treated as an improvised weapon. Creatures that have natural weapons such as claws or bite attacks are proficient with those natural weapons.

Thus, if the creature has no natural weapons, I'd replace the damage dice with that of an improvised weapon and allow normal use of the power.

Any powers that don't have the weapon keyword would be unaffected.

• However, monster statistics blocks often lack reference to natural weapon possessed by usually armed monsters. How about any change in proficiency (read: bonus to attack)? Apr 19 '11 at 21:52
• @Erik If no reference to a natural weapon is there I'd say they didn't have one. Apr 19 '11 at 22:02
• Me too. Then would you impose a penalty to the unarmed attack bonus? If yes, would it be -3 for the lack of a high precision weapon (most blades) and -2 for the others? Should the penalty include the monster magic threshold? Should such threshold be counted on the damage too? Should it be counted only if the weapon is magical? Et cetera... I wouldn't reverse engineer the attack and damage bonuses :) Apr 19 '11 at 22:07
• @Erik For simplicity's sake I wouldn't impose any penalties based on weapon type. I would only subtract any enhancement bonuses on the weapon, and proficiency bonus if it's explicitly listed. But we're outside the RAW now so it's pretty much rule 0 - whatever you can pull off that makes some semblance of sense without slowing the game down. Apr 19 '11 at 22:11

@Okeefe's answer is brief but not very useful--may I attempt a solution based on that fact though?

All of 4e is assuming you have a weapon wielded, so not having it would make gameplay really uncomfortable.

For a player it's just a single action to pick up something he dropped (Minor, move, whatever--depending on DM and feat). I'd just say that the monster has to waste a move to pick up whatever the player made him drop and leave it at that.

I would not actually try to have the monster attack unarmed.

If you must, just off the top of my head I'd lower the monsters attack die by one (D12 to d10, or d10 to d8) and avoid any attacks that relied on it. The attack for player unarmed combat is not much less than armed anyway, and most of a monster's attack damage will come from the monster himself, not from the weapon. (A monster doing 3d10 damage with some massive sword attack would not generally translate to a player picking up the sword)

What you don't want to do is go and recalculate all the monster's stat blocks every combat--that's not going to make anyone happy.

There are no rules for disarming in 4e.

• -1. That is not relevant to the questions. Exorcism of Steel allows a Fighter to effectively disarm a monster, but what happen to the disarmed monster is unclear. Apr 19 '11 at 22:09
• The last sentence of your question: I'm only wondering if Exorcism of Steel is a true exception in the D&D 4th framework or if it has some sort of rule support. Apr 19 '11 at 22:10
• Okay. But that is not a question :) Anyway, I was unclear too: -1 removed. Apr 19 '11 at 22:12