It's true that it's pretty easy for early rounds. I'm stuck at Round 31 (Sapphire Cthulhu) (see post #8). What puzzled me was the irregularity of the the performance of Ultra Rare vs. Super Rare fighters. I found some simple, inexpensive super rare, such as Sapybara, Vinotaur, Flyerfox, Grassquatch, Cactus Kitsune, etc., performed very well. They often rendered critical hits in first try and sometimes gave two critical hits in a row. In contrast, Some Ultra Rare (or expensive Super Rare animals) performed extremely poorly. For example, I tried my Cerberus 5 times so far (combination of Dark and Lightning) and failed them all. From the probability perspective, it doesn't make sense.