HUGE amount of backstory for a few echoes
Well, I have the Temple of Elemental Evil in my game- although the backstory is completely different (I have an elementalist base class imc, none of the GH deities involved- I won't post any spoilers here about the Return!)
Also, the Tomb of Horrors is in there somewhere, along with the Bleak Academy (mentioned in T&B).
I use some setting-specific prc's tweaked to fit (Knight Defender of Forinthia instead of the Great Kingdom, f'rinstance). I'm pretty willing to tweak the hell out of stuff to make it fit my milieu.
Also, there are... "echoes" of my former campaign worlds. Lemme kinda 'splain...
My oldest campaign was set in Greyhawk. Eventually I tired of it and started a new campaign in a new world, Clannath, a kind of celtic-themed world with the overarching villain thing. It eventually developed that Clannath was inside of Oerth, with access controlled via one-way gates high in the Clannath skies.
Now, a good friend and I had some striking parallels between our games and hit upon a "unification" theory. Eventually, there was my Oerth world, my Clannath, and his Zypher setting all unified into the same continuity that involved Tesseract/Kaad, the divine embodiment of gates and portals. There were five very closely tied worlds (one was barely developed at all and one was never developed at all).
Eventually, in my Oerth/Clannath game, Tharizdun got woken up (largely through the efforts of a major pc villain named Fuligin) and ate Nature, pretty much ending the whole thing.
Soo... I started a new, totally homebrewed campaign up a little later. This is called Cydra. BUT it eventually developed that this new world was basically a "simulation" powered by three of the gods of GH (my deities, that is, after an "avatar" style crisis destroyed most of the old gods and allowed for the rule changes to 2e and a whole new pantheon) who were locked in a place called Darkhold, which was outside of Nature and thus had survived Tharizdun's wakening. The Master of Darkhold was trying to build a reasonable approximation of nature; think of it as like a computer model, basically. This was my new campaign world (by this time three or four years old). One of the gods that was locked up was Zelman, the god of illusions. He was a pc from WAAAAAY back in the 1e days; his ascension had been all played out and stuff in another crisis involving Darkhold trying to siphon all the world's magic to fire in one blast at a supermegaultra bad guy. Zelman managed to project himself into the simulation long enough to hand off his staff to a pc illusionist.
Now, one of the staff's abilities (long established) was that it would balance perfectly on the tip of a finger and, if spun, would end up pointing towards Zelman. The pc now in possession of it (Thimbleton) discovered by accident that it would balance and if he spun it it always pointed the same direction. Following it, the pcs found Darkhold.
Of course, without the staff that would never have been possible, and the Master of Darkhold had no idea that Zelman had managed to toss it into the simulation. So he hadn't set up any major defenses; after all, how can a computer model bite the computer? So these pcs made their ways in. While they were in there, as pcs are wont to do, they pulled a mysterious lever and released Fuligin into their world. The Master showed up shortyly after and called them a bunch of names and kicked them out.
Well, Fuligin was an Angel of the Apocalypse. Remember, this was in 2e; he had a strength of 40. Ouch. He set out to ravage and destroy, and pretty much singlehandedly devestated their continent. When it became apparent that they couldn't stop him they returned to Darkhold and pleaded with the Master to help, but his attitude was basically that he'd just make a new simulation. They weren't even real, after all. Finally they convinced him to try to recreate Nature. To do this they had to acquire a number of items (including a "chunk of nature" that turned out to be a gargantuan piece of a moon- like, hundreds of miles in diameter) from the old, destroyed world. To this end they got sent back in time to the end of Nature where they could jump back onto Oerth/Clannath/et. al. and had to gather said items. Of course, the problem was, by appearing at the end of Nature they alerted Tharizdun to the fact that someone had survived. This led to them being pursued by the Angels of the Apocalypse- including Fuligin back in time, before they met him the first time (for them... time travel sure gets confusing!)
Anyhow, they managed to succeed at their quest, return to Darkhold, and give the goods to the Master of Darkhold, who then spent about 100 years making the preperations necessary to recreate Nature. The birth of Nature was the only time Tharizdun could be bound; so, with a lot of hard work and luck, they had managed to defeat Tharizdun. Due to the flexible relationship Darkhold has with time, they didn't have to sit around for 100 years waiting, either. They went back out into their now-real world, found Fuligin massively depowered and so completely broken and insane that he was easy to slay, and set about rebuilding. Whew!
Anyway, point is, a few things changed in the past. Boccob (being pretty much omniscient) figured out what was up, and he and a few other deities that he chose (mostly for their portfolios) secretly hitched a ride to Cydra with the pcs.
So, with a suitable backstory, I have Boccob and a few other GH gods (mostly my own homebrews) in my world as well. Also, since the Master of Darkhold was trying to approximate Nature as closely as possible in the original simulation (which, by the way, was only one of many) there are parallels. For example, there's a Vecna, though not the arch-lich of GH. He does have an artificial hand and eye, though.
Sheesh... talk about a lot of backstory for not too much to do with the thread's topic...