when going for the later badges, there's one trick I found: As soon as restarting gets you to a point where you would get at least 1 brick for another (instant) restart, just do that. Should be around 200 bricks. Restart for 1 brick per 3(+1) clicks over and over again until you feel you have enough to go for the imp badge.
Sadly saving or loading in this game doesn't work reliably. I lost some parts of my progress multiple times already, while other parts seem to be fine. E.g. losing exp and items, but keeping rebirth tokens.
Run up, run right (on the dashed line), get knife (prio 1) or blowtorch (prio 2) upgrades. Very boring, but gets the job done. I put something on the right arrow key, then stopped at 500 coins out of boredom and got all badges. Had 1 move speed upgrade and 1 cooldown upgrade before.
Originally posted by ssgoku7, reposted because it's way too low in the comments and it helped me a lot:
Quickest way to earn the hard badge (takes about 2-3 hours): 1) Do NOT invest in any research. Only purchase the Dart and Laser weapons as outlined below. 2) Area 1-4: Grind it. Acquire Double Shot on Arms and Laser Vision on Core. 3) Area 2-4: Same process. Acquire Triple Shot on Arms and Dual Blast on Core. 4) Areas 3-4 and 3-5. Grind these as well. Simply purchase the additional Spikey Shots for the Arms. 5) You should now be properly equipped to rush through the remainder of the game without any more grind. Hope this'll help with the numerous complaints to make badge acquisition easier. Happy badge hunting!
Addition: Spikey+Triple, Dual Blast and some techs were enough to beat it with parallel monkey on the final level.
I bought everything in free play mode and sent my Hedgehog up to ~60k ft. Then I pressed right for a while and now he is flying for 45 minutes, without me doing anything.