I think the planet vs zombie achievement is broke, went through the whole game and did all 57 towns in 1.5 hours (Loved it so much, i finally beat it after years) but wasn't awarded it
So i did the math, in order for gem LV1 to equal gem LV16, with max upgraded (6 gem for a fuse) it will require 2,821,109,907,456 or roughly 2.82Trillion LV1 gems (6^16) now for unmaxed upgrades LV1->LV16 (12 gem for fuse) you will need 184,884,258,895,036,416 or roughly 184.8 Qa LV1 Gems. now be glad that you can farm for a 0.001% chance and get some gems later on in the game, instead of having to farm and constantly fuse.
i stopped breathing when it came to the last phase, 5 life still there, RAINING YELLOW SHOTS, i cam out with 1 life left, but I FINALLY MADE IT YEAHHHHH
Found a typo in the help section, when it describes the types of stuff, it says ormal instead of normal, just making shure the game is best as it can be.