A legit challenge, due to the aging/reincarnation timing, you gotta find a way to level as fast as you can and make the most out of each cycle. Smart way to balance in challenge by doing it that way.
I've beaten the game a few times. Are you refreshing the shop to grab 10 items each time? speed and power are also the most important stats. swim and fly are good for some defence, but are less important. Ive seen people try and do 1 stat only builds, so its definitly possible.