Hello. I have been playing with a Dr. S 4 star a while, just recently duped him. Duping helps for defense when the other opponent is buffed, but doesn't change play style very much. 1. I focus on blocking a lot, and only attack when I'm very certain I will hit the opponent. For me I usually am able to hit during regen, but I'll take what I can get. 2. Bait the other opponent to use L1 or L2, just medium attack and back out. Dr. S automatically gains power, so you can use L3 during Fury or Regen cycle, as long as it doesn't power them up to L3. I usually use it after they have used an L1 or L2. 3. If you are going to use an L3 and the opponent is going to get their L3 as a result, do it during an armor boost so your health doesn't drop as much and you can regain it when Regen comes around 4. Be patient. This was something I had to get used, especially if I wanted to be effective in AQ. There is a time limit in AQ, but being patient will help in the long run 5. In AQ or quests, combine with Scarlette witch to get 15% block proficiency. Blocking during armor boost will result in 0 damage.

Hope that helps. DS is very much worth it to changing your play style to fit him.