In the endless game mode, I am having trouble winning double prey scenes. Which cards would you recommend to start with and prioritize playing/upgrading.
Double-prey scenes are intended to be significantly more difficult than single-prey! Liz probably shouldn't attempt them until she has a fairly solid deck.
One of the most effective strategies is to take a page out of Madeline's book, focus on Burp cards which quickly deplete preys' Oxygen - they're already taking a Stamina penalty, and will face terrible odds once the available Oxygen drops below 50%.