LoH is outside the rules of D&D, and that's what WRFan is talking about and so am I.
No, you're both wrong, she's not.
The only thing outside the rules is the player/wikiest sneaking a peak at the DMs character sheet.
As for monsters with abilities not encountered in the monster manuals - I present:
CHAPTER 4: IMPROVING MONSTERS
Each of the monster entries in Chapters 1 through 3 describes a typical
creature of its kind. However, there are several methods by
which extraordinary or unique monsters can be created using a typical
creature as the foundation: by adding character classes, increasing
a monster’s Hit Dice, or by adding a template to a monster. These
methods are not mutually exclusive—it’s possible for a monster with
a template (a half-dragon lammasu, for example) to be improved by
both increasing its Hit Dice and adding character class levels.....
CHAPTER 5: MAKING MONSTERS
All the really great monsters, in the D&D game and in literature,
have one thing in common—you can sum up what they’re all
about in just a few words. That’s the first and most essential item in
any monster recipe—a solid and fairly simple statement of what
the monster is all about.
THE MONSTER’S CONCEPT
Before you begin assigning statistics and other particulars, take some
time to think about the basic nature, or concept, of your monster.
Think about the following when working on your concept:
—What do you expect the creature to do in the game? (Is it a
friend or a foe of the PCs? Does it depend primarily on physical
abilities or mental abilities? Is it meant to be encountered once, or
on a recurring basis?)
—Where does it live? (A monster that lives underground may
have characteristics not shared by monsters that inhabit the
wilderness, and vice versa.)
—How does it live? (Is it a predator that relies on its own
strength and speed, or is it intelligent enough to get other creatures
to do its bidding?)
—Does it have any particular enemies or favorite prey?
After you have an idea of what your monster is about, you’ll
have a much easier time making your creature’s type, ability
scores, feats, skills, and special powers fit your concept. It’s okay to
model your new monster on a creature that’s already in the
game—you’ll have less work to do, and your monster will be easier
to use. You’ll find that a short menu of special abilities tightly
wedded to your concept makes the best monster, and it makes the
monster much easier to use....
much, much more - Dungeons & Dragons Monster Manual (Core Rulebook III v.3.5)
... and I have DMed this game since just about its beginning in 1974, including almost a decade professionally at a game store, with literally dozens (possibly over a hundred) of players. I know an unfair encounter when I see one, and this isn't one. I also know how far any player will get with any DM throwing up the Monster Manual (I think asking them if they want to sacrifice a level to Commune with the gods is the niftyest approach).
By the way ...
I recall the fights as hard, but not that difficult.
You might want to talk to this
Thorsson64 guy for some pointers if you think it's extremely unfair.