Wording suggestion:
Slave Driver | Gain a card costing up to $4 other than Slave Driver and play it. If you do, when you would discard it, trash it instead.
| $5 ACTION |
If you gained a Victory card with it, it goes to your discard pile and cannot be put into play, thusly, the second part asking you to trash it will never occur.
Its trashing occurs just before it would be discarded, so any card attempting to redirect a discarded card (
Scheme) would fail. The only thing that could save the gained card is top decking it with
Watchtower (thus causing it to not be played because Slave Driver would lose track of the card) or top decking a Treasure by buying
Mandarin, and such a synergy is very limited, even with
Highway.
Its effect isn't very strong. I would most commonly grab this to use a trashing card like
Chapel so that I would have a slightly more useful card in my deck when I was done. I would drop it to $4 as a
Workshop plus (like
Ironworks): Not to mention it would make its text (that it excludes itself) more logical.