I don't know if this is a glitch or what but I saved up a ton of money and on the last level I spent it all upgrading my base and energy cells. As I was upgrading some of the costs turned negative and then upgrade base turned into $0. So now I can upgrade my base HP as much as I want for free!
just right click and click play, it takes you to the store and it lets you replay your last opponent. I got the hard badge on the second level by doing this.
For the shipyard map i used physical warriors with consecrate, if you upgrade them to max damage they can take the map by themselves.
For the old throne map i just used energy and fire mages upgraded for max damage and 2 physical warriors to take out wave 12.
I just spent 20 hours getting the hard badges in Gem Craft 0 and i play this and get a hard badge in 20 minutes! 11 day walkthrough is very good. On day 5 it should say repair and upgrade water.