The thief-acrobat abilities seem like the perfect example of the kind of 'options' I'm talking about for a class. You're still a thief, but you can choose (at character creation, ideally) if you want to specialise more in traditional thievery or in fancy acrobatic tricks. Likewise, I think the skills of the AD&D / Advanced Labyrinth Lord assassin class could easily and pleasantly be integrated as options for the standard thief. That's another class which, according to my criteria, isn't really necessary - it's just a thief with a couple of skills swapped out.
So I compiled a list of all these thief-like skills, including those from the acrobat and assassin:
- Pick locks
- Find & remove traps
- Pick pockets
- Move silently
- Climb walls
- Hide in shadows
- Hear noise
- Back stab
- Script: Read languages / Use scrolls
- Disguise (as assassin)
- Poisons (as assassin)
- Tumbling (as acrobat)
- Balance (as acrobat)
- Jumping (as acrobat)
(Note that I've not included the assassin's 'percentage chance to kill things automatically' ability - I've always regarded that as a bit over-powered and silly. Besides, it's sort of just a variant on back-stabbing for multiplied damage.)
The script skill, which includes read languages (usually gained at 4th level) and use scrolls (usually gained at 10th level), could probably do with a bit of expansion. Ideally all of these skills would provide some benefit at 1st level. So I'd extend the read languages ability (at a lower percentage of success) to 1st level, and possibly include some kind of code-breaking abilities too, which would be pretty useful for a thief.
Likewise, I'd consider giving back stab a progression of sorts (as it does in AD&D, but doesn't have in LL), so the damage multiplier increases at higher levels.
Also the poisons skill would need some kind of progression - perhaps a percentage chance to analyse or even create poisons?
It'll need a bit of work, but I think it's a pretty promising idea...