Devilites in a boss? I don't want to fight the same, long ranged monster 70 times in a row, and other monsters just wouldn't fit. They'd need some alternate monster types. This would be an interesting modification to devilite levels, but I'm not sure that it is possible to construct 5 sequential levels around devilites.

Just my thoughts on the matter. I think the greaver boss idea would be more easily integrated (t3 boss: greavstricken).

I got an idea for a T3 Fiend boss stratum. Insted, it is the first(and only) Stun Stratum...

May elaborate later....

1 necro of almost 1 year.
2 it has been done to death. please reconsider.

I think it is somewhat an obvious idea as most people might, and I'm not going to say that I've read the entirety of this thread. However I'm going to put in my two cents.

I agree that CEO's typically aren't the ripped guys, so following that logic the CEO himself doesn't necessarily have to be a brute like Vana. In fact you could play on it by having the CEO be a larger, obviously, devilite similar to a pit boss. Who attempts to fire you. When he fails to do so he runs panicked about the room throwing office supplies at you. Periodically he could pause and say "You're fired!" Another thing that could appear in the last stages is the body guards, (I did read some of it) which could be essentially a devilite version of the slag guards that Vana summons. Then you wouldn't have an entirely ranged boss fight. I do think that though he wouldn't be a brute, he would have a speed faster than that of the spiral knights. I do agree that strictly devilites would be bland, so you could introduce constructs as the security system of this inverted building. I also like the idea of having one of the levels be the break room, however that may not fit entirely in with the devilite persona.
I know this isn't entirely fleshed out, but these are what I thought up while reading a bit about this.

So to sum up my thoughts
Stage 1: You walk in, and the CEO declares that you aren't working hard enough, and fires you. When you don't leave he chases you about the room using physical attacks.

Vana's stage 2 and 4 is the floating mask this is where I think the CEO would run panicked about the room throwing stuff at you. Now I don't think the items he throws should be nearly as fast as the devilites current ranged attack speed is.

Stage 3: Introduce a new kind of physical attack, and spawn a few devilites and pit bosses periodically.

Stage 4: Like stage 2 just a little more difficult
Stage 5: The CEO calls in Security periodically throughout the stage, and uses a mixture of physical and ranged attacks.

Impressive physic. I was pretty sure this post was dead when I posted. That's actually somewhat along the lines of what I was thinking for the security guards. I was just tossing out a few ideas though. I just think it would be nice to get a new boss, and some new weapons.