Part 2: Nothing to complain about with the upgrade cost one. Adding other options would be nice as well, such as better pickaxe qualities, weaker minerals, etc.. One other suggestion that I think would be very nice, is another tier-level of gems, up to 20. You can't get them from minerals; only from combining. They would allow you to craft very powerful picks, for a high price (1296 tier 16 gems for 1 tier 20). The only problem I've noticed so far is that sometimes the auto-sell button for the pickaxes will throw away pickaxes that are better than the one equipped, for no reason I know of. If the automine is better, it always stays in the inventory. However, if the damage is better, it won't always stay in the inventory. I'm not sure what causes it, but it can get pretty annoying knowing that a few amazing picks have probably been passed up simply because the game didn't think they were better. Perhaps judging them on overall DPS would be better? (Whichever has the highest DPS stays)
Very long comment(s) inbound... Suggestions for rebirthing: Bonus Damage should be more exponential. Start out at around +10%, but make it curve out to a more valuable number the higher the cost to upgrade it goes. Armor penetration is fine (99.98% max, there's nothing you can really do with it anymore). Starting gems/ starting gold is great for rushing to your next rebirth, but fails to make any use of itself outside of that. Perhaps make higher upgrades give higher gems? The starting gold could be exponential as well. The base combo upgrade is a good idea, but because of how useless active farming becomes after a while (IE it takes 1 second of idle farming to make up for 100 seconds of active farming), this upgrade is also useless. I suggest a re-working of the active damage system, allowing your active damage to raise up to an even level to that of your idling capability. This would fix the combo problem, I believe.
I'd love to see the total amount of energy being removed from the reactor. There comes a point in the game where placing one cell can potentially instantly destroy all of your fans, and then instantly blow up the entire reactor right after.
At first I was really pissed off at this game because it seemed so broken, and the dev didn't seem like he was responding to anything, and simply making the game more and more broken. However, having been with nooze for a couple days in chat now, I can tell you firsthand that he has been working his ass off to make this game perfect... he makes several updates a day to balance things out, and constantly gets new suggestions from regular, late game players. This game isn't easy to balance out, so give him so leniency before you go saying this game is bad!
The top scores for speedruns seem a little absurd... 711 seconds? I mean, even 875 seems impossible. I can imagine shaving 3-4 seconds off of each of my runs, and possibly 35 seconds total time, but that still only leaves me with a 901 second speedrun of the entire game. I just don't see how it's possible that all of the scores below 900 seconds are legitimate.
To be honest, I liked this game far more when there were infinite upgrades for equipment. I realize that you made a limit because users could reach neigh-immortal status, but a simple solution could just be to make future upgrades less effective. IE, all upgrades past 15 are 50% less effective, past 25 are 80% less, past 35 is 95% less, etc.
Tukkun -- I have never seen a game developer with a better attitude towards hackers than you. Instead of banning all hackers immediately on sight, or making it harder for them to hack like most developers do, you simply ASK them if they're hacking, so that their scores will not be submitted if they are, and they are thus allowed to continue on hacking without affecting anyone else... It's beautiful. 5/5 would play again.
This game was a good way to innovate the Boxhead series, but there is ONE MAJOR FLAW: You can't customize ANYTHING before the game begins. Remember Boxhead: The Zombie Wars? You did that correctly. Before the game started, you could set the difficulty, the types of zombies that spawned, what your starting combo was, if there were things placed down beforehand, and basically ANYTHING you wanted. Here, it's NOTHING. You just click the map and it puts you in there. From what I've seen, there is no way to customize anything before the game starts at all. I hate those damn teleporting zombies; I would always turn them on in Zombie Wars because if too many teleported at once, you'd find yourself being gangbanged by about 30 of them every single time you spawned out. Here, you just have to accept the fact that you can't get rid of them. Sometimes, I loved playing with no devils, teleporters, mummies, or whatever else, and I would just play with the classic zombies. Here, I can't do that.