Any Dmg reducer will do this. Slyde is a good one, also Steve i believe.
If your ever having trouble with an LD mission, go look at the card and there is often atleast 1 post on what to do to complete the missions
If it helps I had Denise (awful card) and Slyde when I did mine. Just put them out there and intentionally lose the fight. Steve is good to, if you happen to have him.
Use a deck made of damage reducers and you should be done quickly.
How do you get fourth mission? i try but i don't know to improve that.