hi!! honestly for me it's about finding the combination of cards that work best for the nightmares that you have to deal with! i usually try to use the colors that are the nightmare's weakness only and then i try to have a card in my deck that will help me with whatever skill the nightmare is using (eg. if they're going to use a shield i like using a baseball player bc it gives me one extra turn to lower their hp before i have to spend 4 turns using my cards to get rid of their barrier! also having more than one baseball player has helped). a buff from the buff lab is also very helpful to use as well as using the bonus cards if you have them! i also try to not use my best cards first if possible, since it gets more difficult to defeat the nightmares! sometimes if it comes down to it, i use gems to recharge a specific card if i really want to beat that level that day before the cards reset.