Personally, I'm stuck on Divine Greek Gods cards. To get the first one, I spent a third of the deck on it. First, I spent all the Mythical Beasts, making about 120 million hits. Then most of the weapons. I have never reduced the attack :) After that, I started the standard tactics: tank, shield, three dds. The dd with an attack of more than 100k ran out very quickly. I had to take Greek Gods. I lost almost all of them, but in the end I won.
Now, to get the second one, I need at least a sixth battle slot. And to do this, I will first need to restore all the weapons (1-2 days at my pace), then start the feather farm (6-8 hours of autoclicker) and only then can I repeat the procedure. And I'm not sure I can handle it :)
Have fun! :)