D&D 5E Wall of Force Reality Check (as used by DM not players)

There are a lot of threads about the Wall of Force ("WoF") spell and how DMs can avoid having it break their games. But I'm looking for feedback on my intended use by a monster and my understanding (or lack of understanding) of the RAW for this spell.

In an upcoming game, the party will need to infiltrate a mind-flayer colony, where they will encounter an elder brain (EB).

I'm interpreting the EB's glass-like protective layer (described under Elder Brain Resting Pool in Volo's Guide to Monsters [VGM] page 78) to be a WoF cast as a lair action (VGM 173).

An EB can keep recasting the WoF every turn if it needs to. If it loses concentration, it just has to recast it on initiative count 20 the next round.

So how can the party harm the EB? Here is how I interpret the RAW for WoF. I'm interested in whether you think I'm interpreting them correctly. Yes, yes, DMs can interpret and implement rules however they want, etc. But my players are tactical and we enjoy a bit of rules lawyering. Hand waving things like this isn't very satisfactory. Ultimately, I'm the judge but I want it based on a reasonable interpretation of RAW.

So, with that said, I don't have any issue interpreting the first paragraph of the description of the WoF spell. It is the second paragraph that I want to make sure I'm getting right:

Nothing can physically pass through the wall. It is immune to all damage and can't be dispelled by dispel magic. A disintegrate spell destroys the wall instantly, however. The wall also extends into the Ethereal Plane, blocking ethereal travel through the wall.

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My anticipated rulings:

1. While the WoF covers it, the Elder Brain is immune from any weapon attacks. Nothing can slash, pierce, bludgeon, etc. through the WoF to damage the EB.
2. There is, however, nothing in the description that indicates that the wall is immovable. In other threads I've read, everyone assumes it is. Why? Where is that stated? Nothing can pass through it. Nothing can damage it. If you have a WoF sphere surrounding you, why can't a giant kick it (and you in it) like a ball? If a dome, why can't it be lifted? Force is "pure magical energy focused into a damaging form." (PHB 196). WoF force is not a damaging form, but pure magical energy focused into a form. Otiluke's Resilient Sphere is a "sphere of shimmering force" that can be pushed, rolled, picked up, and moved by other creatures.
3. Since a Wall of Force should be movable, with a big enough hit, you may cause the EB to smash against the side, basically causing an Elder Brain concussion. A smart EB will have the inside of a WoF sphere filled with brine, which will mitigate that, but it should be one non-magical way to cause some damage. I'm thinking that if a player rolls a crit, they jar the EB within its WoF enclosure so hard that it take half the normal damage of what the hit would cause if it was made directly to the brain.
4. "Nothing physical can pass through the wall" includes energy and magical forces (where "force", "energy" or "light" are used in the description text. So most attack spells will not penetrate, but something like Vicious Mockery would cause damage through a WoF. This also ties in with the EB's protective layer as described in VGM which states that psychic attacks can pass through. Other spells I would think could be used to harm or control creatures behind/enclosed in a WoF include: Weird, Banishment, Tasha's Hideous Laughter, Slow, Sleep, Power Word Kill, Phantasmal Killer, Phantasmal Force, Otto's Irresistible Dance, Modify Memory, etc.
   
   Many of these are illusions, and psychic in nature, which integrates well with EB lore in VGM. But I think it also gives options to those who think WoF breaks the game. If you have a Mystic or an Illusionist, they can still mess you up while you're cocooned in your WoF.
5. It goes both ways. Nothing physical can pass through. Any attacks or spells that cannot enter from the outside, also can't come from the inside and go out.
6. Concentration. WoF is a concentration spell. Those who claim it is game breaking don't seem to show much creativity in the myriad of ways concentration can be broken. Besides taking damage or casting another concentration spell, you could create distracting illusions, cause confusion and chaos on the battlefield, "push their button" causing them to lose their temper and concentration. EB are so full of themselves that they may lash out if mocked and belittled, given a high enough skill check.

Reading other threads that complain about players having this spell makes me think I'm missing something. But I see a number of ways to deal with WoF. Here I'm not worried about players breaking the game with it, but that it doesn't make the encounter impossible...to more I reread and think about the WoF spell, the more I think it is not the impossible-to-overcome broken spell so many make it out to be.

Let me know if I'm way off base or missing some nuances.

There is nothing to indicate it moves. You create an immobile wall of force energy that can't be moved by either the caster or anyone or anything else. Otherwise players could move the wall around like a mobile barricade or catch stuff in it and move it around. That is not indicated in the spell, so I see no reason to add that functionality to the spell.

Concentration is not a hard roll. Illusions to my knowledge do not disrupt concentration, only damage does. It takes pretty substantial damage to disrupt concentration for a lot of casters. Though powerful AoE is quite effective at doing so.

I would not say a Wall of Force can move. I think the spell would say so if it could, in particular since it says the wall can be free-floating. If it could move, then presumably a wall with no supports would fall.

But there is nothing to say that the WoF variant that the brain is using cannot be moved. That would give the non-casters in your party something to do.

Still it will be the case that the difficulty of the encounter will depend very much on the spells the players have prepared. I would worry that if you don't give them some forewarning, the fight will be frustrating for them.

WoF is a kind of absolute spell.
The elder could use it to entrap himself but it would be more nasty to entrap one or more PC, and continue fighting the others.

And I would not rule that vicious mokery be able to pass through a WoF.

Can u cast a Sacred Flame through a wall of force? I mean, it's not a ray or a line, or a cone, it's just magical energy appearing on your target? See for example Forcecage, which clearly states that no spell can be cast through it. Wall of force does not say that.

Delazar said:

Can u cast a Sacred Flame through a wall of force? I mean, it's not a ray or a line, or a cone, it's just magical energy appearing on your target? See for example Forcecage, which clearly states that no spell can be cast through it. Wall of force does not say that.

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I'm not claiming it is the intended way to do things, but the way I have always handled it is that a wall of force stops only effects which actually physically travel from the caster to the target, whatever that target may be.

So while the "bright streak" of a fireball spell will hit the wall (and explode, again, my ruling not necessarily the intended one), or a lighting bolt will stop when it hits the wall, a spell like sacred flame that originates from a different point isn't hindered because - as you mention, unlike force cage - the wall of force spell says nothing about preventing that from happening.

Leomund's Tiny Hut actually seems to do a better job of describing how the impenetrable barrier operates. I'd suggest using the one to inform the other.

Tiny hut looks even better than Wall of Force defensively. Go against big boss, cast tiny hut with the whole party inside. Then one by one, get out, attack, get back in. Lasts 8 hrs, no concentration required.

Casting time is long though, isn't it?

Delazar said:

Tiny hut looks even better than Wall of Force defensively. Go against big boss, cast tiny hut with the whole party inside. Then one by one, get out, attack, get back in. Lasts 8 hrs, no concentration required.

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The caster can't leave the hut, so that's an issue. Well, that and if someone tried to do that I'd have readied bull rushes and grapples. Or bury the hut. Or dig underneath it (it does not specify a floor). Or just have everyone ready to kill the next person to step out.

I would rule that a wall of force would stop any spell that had a range or area of effect, I would treat it like a normal wall as far as providing cover.

From page 80 basic rules
A Clear Path to the Target
To target something, you must have a clear path to it, so it can’t be behind total cover.