Deducting points on multiple attempt questions

Storyline assigns the score for a score-by-choice question based on the amount entered in the Points column for whatever the final answer is. 

If you want to deduct points for extra attempts, I think you'd need to set up a disguised question slide. In other words, the user would click buttons that aren't the official responses. Submitting those answers would trigger the selection of the appropriate official, hidden response. 

This projects demonstrates and explains how to give partial credit for a Multiple Response question. That's not exactly what you're doing, but it might help you understand what I'm suggesting. DEMO: Giving Partial Credit on Multiple-Response Questions | Review 360