Does Luck show up in the dice rolls on screen if you enable that in your Options?

Anyway there is very little information on Luck floating around. In the Manual under Fatigue it states a -1 Luck penalty gives a -1 to all rolls the character makes.

Under the Luck spell it lists Saving Throws, Thac0 and thieving skills (succesful Pickpocket, Find Traps etc) and under Bard Song it lists damage as benefitting from Luck.

What other rolls are there? In DnD pretty much everything is a die roll but how much is covered in the IE engine?

As it stands a Luck bonus seems to be a pretty powerful bonus that's not made much use of (except as BardSong!).

It influences to hit rolls (I don't think it improves THAC0 per se); you shouldn't see it in the character record but probably will show up as a to hit modifier when enabling the combat feedback. It may influence other stuff, but I wouldn't count on any huge differences.

Note that luck is the primary penalty for fatigue and intoxication, so it is actually used as a basic engine mechanic. BioWare also gave some creatures default luck bonuses (a cheap and dirty way to make them slightly tougher).

Despite the manual, I don't think that Bard Song actually has any effect on characters' luck stat.

Luck spell may work the same as the luck stat, but it's implemented as a separate (non-cumulative) effect that doesn't actually modify the stat (or does so at a lower level).

Right so regardless of your current Luck the spell will set your Luck to 1?

In what way can you influence a to hit roll without improving it?

Again the effects of Luck with regard to Fatigue and Intoxication are meaningless if Luck doesn't affect at least some actions performed while Fatigued or Intoxicated right (such as tohit rolls, pickpockets)?

I suppose I can test Luck with regard to Thac0 easily enough but with regard to other actions (especially thieving) it's not so easy to see.

As stated, luck affects at least a character's to hit rolls. The penalties can be overwhelming when severely fatigued or intoxicated.

You should be able to test its effects on any of the other skills by getting a creature that can almost always successfully perform some action (say, picking a certain lock), and then applying a luck stat modifier effect with a large penalty (or just waiting until it's really tired or really drunk) and seeing if there's any difference in the same action. (I think the luck stat is a signed byte, so don't go less than -128 when choosing a penalty value.)

The non-cumulative luck effect (not the same as the luck stat modifier) probably behaves in the way you'd expect (it doesn't stack with itself, but stacks with any effects from the luck modifier). I'm not sure if there are any differences in the actual effects (it may exist only as a way to make the luck bonus non-cumulative).

There is also a damageluck stat, though this is barely on topic

Seeing as Luck isn't in use that much I guess DamageLuck would be of limited use!

How many effects remain unknown?

For BG2? None.

318 to 457 have no description in my DLTCEP, is there a new effects description dat file with those listed in it anywhere?

There are only 318 effects (0 - 317; actually less since they skipped a bunch, but close enough).

Yeah, Avenger goes all the way up to 457 or so, as IWD2 has that many opcodes (well, the opcode numbers go that high. There are a boatload of unused ones).

0-317 is the opcode range for bg2 with 3-4 that outright crashes.
There are only a handful (around 10) that are completely not working, some have been confirmed to be totally empty, some modify unused stats, some do something obscure (still need research).
All bg2 opcodes are known by name (thanks to DevSin) but some might have some obscure options not found yet.
(Like how many of you know the current hp opcode can outright resurrect or remove effects)

Known values for 'Mode' are:
0 Heal normally
1 Cure death
2 Remove effects
3 Both

Damageluck ensures minimum damage caused.

Remember that the remove effects bit only works in ToB (CTRL+R only heals dead in SoA, and this was all that the heal effect implemented there).