Use the percentile skills as given but let the player add the entire score for the relevant ability to each skill. So for example you begin with a Move Silently skill of a paltry 20%. But using this house rule you can add Dexterity to that number. So if your Dex is 15, you're rolling 35% at first level. Still not fantastic, but much better than by the book.
|Thief char sheet I drew for Blueholme.|
Open Locks - Dex
Remove Traps - Dex or Int
Pick Pockets - Dex
Move Silently - Dex
Climb Sheer Surfaces - Dex or Str
Hide in Shadows - Dex
Hear Noises - add Wis modifier
I also strongly suggest taking Cook/Marsh up on adding these skills to the Thief right from level one. Mentzer didn't include them because he thought they were stupid. Mentzer was wrong. I wanted my ventriloquism.
Climb Ceilings and Overhangs - Dex (as Climb Sheer Surfaces minus 20)
Ventriloquism - Int or Cha (as Move Silently +10)
Distract - Cha (as Move Silently)
Mimicry - Int or Cha (as Climb Sheer Surfaces)
Ventriloquism would work more-or-less like the spell. Distract would cause an enemy to lose initiative or get a -1 on their next attack. Mimicry would fool someone into thinking they were hearing another person or animal.
This is not the first time I've had thoughts about Thieves. Nor will it be the last. As long as the record stands that old school D&D Thieves suck there will be rants about it, not just from me but from everyone every day all the time.
Here I am talking about it in 2015.
And in 2016.
And I revisit the topic in 2019.