OK here are my initial reactions and thoughts.
1. General Stats
Your HPs and Defences and Stats seem to be a bit off. The creatures Stats especially seem to be quite a bit higher than they should be, it is a very clever and incredibly charismatic undead wall (with these stats it would be a smash hit at dinner parties
).
Using your (inflated) stats I get its HP and defences to be:
HP: 240;
Fortitude: 26;
Reflex: 21;
Will:25
2. Grasping Darkness
I get this to be:
Reach 2; attack +12 vs. AC; 2d8+7 damage; on hit target is grabbed (escape ends)
One potencial problem for your grabbing wall here is its low Reflex defence, which means that it will be easy for Acrobatic characters to escape its clutches. While its inflated strength is pumping up its Fortitude defence and making it much harder for Athletic characters to escape. This might need thinking about, you could maybe state the target DCs in the attack power.
3. Scrabbling Throng
I think I understand what you mean here, you are trying to give it a lesser version of Threatening reach, in this case if a creature moves three consecutive squares within reach 2. Personally I think this will need reworking as the first time it gets this attack off the players will surprised at the new attack mechanic, then they will just learn to hop in and out of its reach. This power will also be a bit fiddly to remember turn after turn, so you may get inconsistant results. I would say a creature either has Threatening Reach or it doesn't, and in my opinion Threatening reach should be a rare power.
4. Macabre Devouring
I wouldn't give this creature such a high damage attack as a minor action when its basic attack is already using the high damage matrix
My usual way of dealing with this sort of attack is as follows:
Macabre Devouring (minor; at will) -
1/round
Target must be grabbed at start of Walls turn; attack +10 vs. Reflex; 2d6+7 damage
5. Swallow
It seems a bit cheap to have this as a move action when it is such a nasty attack, but I don't have any real objection to this.
Again it should be attack +10 vs. Fortitude
6. Bonealanche
I like bonealanche it's amusing and logical, and it makes an impression on the enviroment (the difficult terrain).
Again it should be attack +10 vs. Reflex
General
As I have stated your to hit values seem off, a level 9 brute should be at:
+12 vs. AC; and +10 vs. Fort/Ref/Will
I like the idea of the wall of bone, but as previous posters have said it is massively weak against ranged attacks and could be pumelled by a bow ranger/wizard/warlock/cleric. As it can't move you might want to add an ability that states that it cannot be subject to push, pull or slide effects, or knocked prone (etc)
The wall is undead, maybe it should have some resistance to necrotic and vulnerability radiant.
What I would do with this encounter is design some sort of caster that specialised in push,pull,slide effects so that you could drag the PCs into the reach of the wall. Or you could have some sort of crushing wall trap behind them that slowly forces them forward each turn, limiting their ability to stay out of reach. Then of course there is the obvious, it is blocking the passageway ahead that they need to go down, so they
have to engage it.
Anyway these are my first thoughts, I hope they are helpful.