Anyone has like general tips on what to do for this game? Been trying to breed more with positive traits but couldn't get enough fighters from wave 6 onwards...
Okay, first, selective breeding doesn't work. Most likely, because it wasn't completely implemented, and we'll see it work in later versions.
Second, put a mix of different kind of defenders. People in this thread don't agree about what is the right mixture, which probably means the game is reasonably well-balanced.
Third, it's a good idea to expand production of your goblins. At least to the level of getting an entire new team of defenders every day. You can, and should, replace killed goblins right in the middle of battle.
Fourth, you can have a single goblin impregnate 3-4 women, but you would be too busy with other things to do it regularly. So give every woman a dedicated goblin to impregnate her. And have dedicated women nurses too. Or maybe shortstack nurses, since they don't seem to be very good in battle. It's all about minimizing the need for your attention, because a lot of things need it.
Fifth, if you don't have enough women, you can have MC breed one of the ones you have. Shortstacks also often give birth to women if bred by MC.