Drow -
Since they reside in the earth and seldom tend to venter elsewhere, have there skills modified to work only in undergroud/underdark/inside areas. Much like a ranger cant sneak and hide in a city or a thief outside.
Orcs -
Since the only place an orc can call home as of the moment is the Village(maybe ZK too) modifing the skills to work like that of a ranger would be better.( ie sneak/track/hide work only outside)
Half-orcs -
Eventually, when they make thier home Skullport the same udergroud restrictions of the drow would apply.
Basically its the same class except for (A)the name change from thief to scout, (B)the pluse/minus of a skill or two, and (C)race specific conditions.
(A) - much like the barbarians vs fighters, basically the same guild just that the names changed and so forth on the players score card and what ever else.
(B) - I don't have a thief PC so I don't exactly know all the skills given to them so I can't give a detailed referance of which ones should be dropped but steal is #1. Added though, track would be definatly. Also to be taken in mind that this is to be race specific, Orcs are to would not care for the subtleties of a backstab nor are they smart enough to read off scrolls...
(C) - Since these guilds are for tow specific races, barring outsiders from joining and preventing their flock from joining outside the giuld is prudent. So only Drow can joint the Menzo/skullport chapter and they can't join the thieves guild in ZK, even if they're still a rouge. Much like a Halfling can't become a bard. And sthe skills are race modified, SO
A work in progress, will add to with clairity...
