User blog comment:Zombie8888/insanity challenges/@comment-4111680-20120510051757

Numbers 1, 2, 4, and 5 are impossible. #1 would take hundreds of years to complete. #2 is way beyond the 32-bit integer, 2147483647. #4 is impossible as Dr. Zomboss's Revenge takes about 15 minutes per round, totaling a total of 25 hours necessary to complete the challenge. #5 goes by a similar logic: 2000 Zombatars taking at least 2 minutes apiece, or about 66 hours.

Otherwise, #3 is way too simple; just wail on it during Vasebreaker Endless. #6 can be done with the Sunflower and Kernel-pult alone during a revisit of Adventure Mode. And some master elite hacker might do #7. :)