[D&D 3.5 E6] Off-the-cuff Encounter: What am I?

[Gan The Grey]

I'm currently running my players through an ancient temple complex in the middle of a ruined city. They've made it into the courtyard, and are now looking for a way to raise the front gates so they can pull their cart inside. I've got the barbican and connected rooms mapped out, but I don't exactly have completely specific ideas as to everything they will encounter within. Whilst exploring the western wing, the group came upon a small prison area, and I hit them with the following, off-the-cuff setup:

"Rust-flecked iron bars block entrance to a small, compact prison area. A narrow hallway extends beyond for some fifty feet, framed on either side by a similar family of barred doors. Though a scant handful hang ajar, most stand securely closed. As you move past, you notice a pair of manacles fastened to the rear wall of each cramped holding cell. Rust has eaten them into near uselessness. Strangely, the state of the manacles mirror the state of their doors. In the locked rooms, the manacles hang closed. In the open rooms, the manacles are equally so. (A Wisdom roll tells them that whenever this ancient race vanished, they were likely kind enough to take their prisoners with them.)

As you near the end of the corridor, a wave of goosebumps afflicts each of you in turn. The final door bears no bars. No, this narrow hall terminates into door of the hardest steel, thrice reinforced to ensure impregnability. Unlike the other doors, not a single speck of rust mars its facade. An uneasy feeling descends upon the party as the key slides in and smoothly releases the ancient lock.

The door swings in on a fleeting darkness before the light from your torches washes over a terrible sight. The body of some great mummified creature hangs opposite the door, its four arms stretched wide and steel-bound to the far wall. Three dessicated eyes stare at the floor from within a alien skull, a skull that seems to grow directly out of the top of creature's substantial chest. Scraps of rotted clothing still cling to its husk."

I ask them to make a Fort save, of which only one of the three pass. The two each gain a negative level. They immediately shut the door. A detect magic spell reveals a residual negative energy effect.

I haven't designed this thing and don't have much of an idea what to do with it. It's interesting though, and my players are hooked. We ended it right there. So what should I do with this thing? I was thinking that maybe it wakes up once it has absorbed four negative levels, but I don't know. I'm looking for ideas. What was it originally? Why is it here? What is it now? What can it do? Why did the party gain negative levels by just looking at it/opening the door?

Work your creative magic, Playground! Oh yeah. Please. I heart you.

[hierophant]

Hmmmm, very nice.

Whatever it is, I'm thinking that the energy it absorbed, though not enough to revive it, allowed its presence to be sensed by its creator/mate/children/etc.
If the PCs don't act quickly, it will be revived for whatever nefarious purpose it was initially created.
Of course, if they do act quickly, someone will be tracking them down for revenge.

Life-draining aura - maybe it's not actually undead, but drains the positive energy out of others to fuel itself. Could be a nice twist on the obvious.

[Gan The Grey]

Well...thanks for the reply. Doesn't look like I'm going to get much more help though.

[Baphomet]

What level is the party? My first instinct was some kind of Abomination, but those might be above your party's appropriate challenge rating.

[Gan The Grey]

What level is the party? My first instinct was some kind of Abomination, but those might be above your party's appropriate challenge rating.

Level 3, almost level 4. E6 game, just to reiterate. I'm probably looking at something fairly custom here, but I'm not looking for just a stat block. I'm looking for interesting history and such, the 'why' of this thing's captivity and what it can do/wants. It's more of a side-quest overall, but my players are really interested in it.

Edit: Level 4 Knight, Level 3 Duskblade, Level 3 Bard. Low to mid optimization.

[Amechra]

Please, I adjure you, adapt this to your needs.

Because quite frankly, that is the first thing I thought of.