My piece of advice for the hard badge... don't buy any upgrade for additional hero classes but the marksman one, this way you'll get only riflemen and marksmen in battle; with a full team half marksmen-half riflemen + shotgun + airstrike + colonel upgrades, reaching 3km in endless mode becomes almost easy.
I finally got my "ret-hard" badge, meh... resupply, static shield, ion cannon, holy grail, pulsator, acid hound, power extender, adrenaline boost, combat armor, hair trigger, they all can help depending on the mission. Still too frustrating tho...
I wonder if creating a game is really this easy... otherwise I couldn't explain why someone would waste time and efforts into a game and then going all the way ruining it just cause of greed. And it's not like it's the first time, I've played Sorcery Quest for quite awhile and I've been a token user there until they started to ask for my inner organs (don't know about Critter Forge, but I guess it's the same). I mean, you make a game with a nice colorful graphic, with original and addicting gameplay and then you decide to ask for tokens for every single breath players take while playing; with less asking for tokens all of your games would have a lot more players, a 4.5+ rating here on Kongregate and you would have a better reputation and probably even a better income than now. I know you can play without tokens if you want, but the game loses all its enjoyableness that way. Just saying.
Just build spear towers wherever you can, use ice/poison traps if necessary, put your points into mana and gold; you'll win any lvl with 3 stars rating, no matter what pet you choose (pick the mana one btw, the other 2 are useless).