So, it's kinda nice to be on this side of all that work. I now have 12 Scoundrel abilities and seven skills, available to all classes. Nice.
Also nice, in my opinion, is how easy this system is to adjust. As the ref, do you not like a few of the abilities? Strike 'em; there's plenty more, so there will be plenty of choices left over. Want other abilities? Add 'em. Don't like d12s? The skill system will work well with most dice, I think. d4s and d% probably wouldn't be so great, but I think the skill system would probably be viable with anything from a d6 to a d30. Don't want the skill system at all? There are enough Scoundrel abilities that a ref could, if he wanted to, yank the skills and still have plenty of choices for viable Scoundrels. (Of course, he'd have to find another way to adjudicate things like picking locks… but we've already had that discussion.)
Anyway, I think I'm almost done, but there are at least two items I still need to address. The first is how to adjudicate abilities. I really like the mechanic I proposed for the magic scrolls in an earlier post: to succeed at the ability, roll at or under the relevant attribute + character level +/- relevant modifier. Of course, refs could substitute their own methods of adjudicating, ranging from harder methods to just ruling that the Scoundrel succeeds whenever attempting an ability. Personally, I'd probably use a mix of automatic success and the attribute+level+/-modifier system. Backstab, for example, should always be automatic, while there should always be a chance of failure for using magic. In between those ends of the spectrum, I would probably rule that ability success is automatic when not trying to do something super-hard or super-quick or with resistance. For example, letting a Scoundrel automatically succeed in doing first aid on another character after they are safely back in town, and when the character was only down to 80% of their hit points in the first place is something I'd see as reasonable, while trying to keep a character from dying in the middle of a battle when they just had their leg chopped off because they rolled poorly on the Table of Death and Dismemberment would require a roll, I think. As another example, earning a little money on the side with sleight-of-hand when not adventuring should be automatically successful, while keeping a ring hidden from some guards that are searching the Scoundrel should require a roll to succeed.
The second is what happens when a Scoundrel fumbles when trying to use magic. Going the way of DCC and having a chart for each spell is… for more dedicated men than me. I'm thinking a simple chart could work for most, if not all, spells. Something like…
1: Roll again on table 1d4 times and combine results
2: Change target to self/enemy as appropriate
3: Change target to ally/enemy/self as appropriate
4: Increase scale of spell effect
5: Humorous effect only thematically related to spell
6: Reverse spell effect
Actually, let's stop here and open this table up for some Gygaxian Democracy. Post other very, very general ways that spells could go wrong in the comments and I'll (probably) include them (and credit you) in the final result.