Half Black Dragon Fire Souled Troll-Blooded creature?

[Rossebay]

Comes back, no matter what, unless hit by a save-or-die, right?

Or am I reading that wrong?

Regeneration to everything but Fire and Acid, and then Fire&Acid immunity. So my character would always come back?

[Starbuck_II]

Comes back, no matter what, unless hit by a save-or-die, right?

Or am I reading that wrong?

Regeneration to everything but Fire and Acid, and then Fire&Acid immunity. So my character would always come back?
Correct.

Greymantle is a spell that takes away regeneration (all types) if fail save. So you have to make your saves or someone might cast that spell (eventually).

I forget which 3.5 book has that spell.

[Rossebay]

Oof. Alright. Well, there's got to be a way around everything, right? Haha.

Anyway, thanks.

[Anxe]

Also, Searing Spell, Fire Shield, and other such shennanigans.

[Ernir]

This is one form of what is known as an "IKEA Tarrasque".

Google "Emerald Legion" for a more complete example of the concept.

[Keld Denar]

There are other ways to deal with it. Ability Damage and Energy Drain still work. Polymorph effects still work, such as Baleful Polymorph or Polymorph Any Object. As you mentioned, Death effects still work. Disintegrate will work, assuming you reduce the creature to enough negative HP that even on a successful save, he'll still take damage at >0 HP and get dusted. Starvation and drowning still work.

Unless you figure out a way to give the creature immunity to non-lethal damage, you can simply knock it down so far in the negatives it'll take a month to wake up, and the creature will starve to death while it regenerates. Or just dump the body in a pool of water. Without being consious, it'll immediately start drowning.

If this is a player's character, do note that even though the character is rediculously resiliant, his party isn't. If a group of NPCs kill him, then the rest of his party, they'll either have as much time as they need to deal with his regenerating body, or they'll simply loot him, his allies, and leave him naked. Just because you are more or less immune to death doesn't mean you are immune to losing.

[MrRigger]

You're also still vulnerable to Trollbane, the alchemic item from Dungeonscape. It's an injury poison with no save that suppresses regeneration. Apply it to the ubercharger's lance, and the guy is dead.

MrRigger

[Jack_Simth]

Comes back, no matter what, unless hit by a save-or-die, right?

Or am I reading that wrong?

Regeneration to everything but Fire and Acid, and then Fire&Acid immunity. So my character would always come back?
From simple damage that's not in ludicrous amounts, yes. However, as others have already mentioned...

1) There's ways around Fire Immunity.
2) Nonsimple damage can still get you (negative levels, death effects, ability damage, ability drain, disintegration, and so on)
3) Ludicrous amounts of nonlethal damage will still kill you... via starvation / dehydration, which regeneration doesn't foil.
4) There's ways to get rid of regeneration (Trollbane, graymantle, et cetera)
5) There's ways to lose for good without actually dying in D&D (Flesh to Stone, Baleful Polymorph, Trap the Soul, Dominate Monster, and so on).
6) Just because you recover, doesn't mean you win. You've got... what, +4 LA there? ... without some hefty cheese on top of that, you're basically baggage to the rest of the party.

Now, if you've got free LA, you're doing this in Gestalt, or some such, it can be useful... but for the most part, it's rather "meh" until you also get something to ignore the effects of nonlethal damage, and deal with all the above.

[KillianHawkeye]

Disintegration shouldn't work on a creature with regeneration, because it never reduces his actual hit points. Instead, regeneration converts the damage to nonlethal damage, which counts up from zero. Thus, the "any creature reduced to 0 or fewer hit points by this spell is entirely disintegrated" clause is never triggered. The end result of a failed save to a Disintegrate spell would be a creature at maximum hit points with CL*2d6 nonlethal damage.