Does Felicity have a 1-2 turn boss killer build, like the other 3 have? She can plow through everyone else easy enough, but she struggles the most of the final boss in hard-mode.
Yes, each and every one of them has a build that's completely broken, and can kill any boss on the 1st round.
And I'm saying this WITHOUT even mixing cards from other heroines - Just by using only their own cards.
You need a compact deck usually, meaning that you should not have more cards that don't draw more cards than your hand can hold. That way you will never run out of cards. 0 cost cards and energy supplying cards work well with this strategy, as well as any items that boost your 1st turn efficiency (Blond has some great ones).
With Felicity, IIRC, you should use cards that gives you plenty of that debuff that takes away your energy on the next turn (forgot the name), you won't need a next turn anyway, then you chain cards that give you explosion relative to the amount of the 1st debuff, build up a ton of attack like that, than use something like the kick card that gives you more and better kick cards as you use it. With "genes" added to the cards, I defeated even bosses just by powering up - I didn't even get to the attack part and they died from cards I modified to give a small attack. The game balance is totally broken with some builds, but it's fun to find the builds that brakes it.