Neoverse

If you haven't earned this one by accident, there are a number of good choices. The best of these though, is to find an enemy that can give you the card 'Infinite Growth'. Every time this card goes into the card pile, it splits into 2 copies of itself. Once you have lowered the enemies health to about 20%, simply play defensively until you know there are 10 of these in your deck, then finish it off. Try not to let them get out of control though, as once you have more than about 6 of these, they love to escalate very quickly, meaning you can spend whole turns just discarding them, and still end up with more.