Reminder: You do not need to complete all levels to get the hard badge. Just level 40 needs to be completed. Though to be precise all i can say is: I skipped level 37, completed all others and got the badge. Hm...ok, i will try 37 again now. ;P
As for the hostile arena: Why does it end after wave 5, though there are 6 mentioned? Why does it beep at the end-score-screen as if the next wave is starting? And why does it show "0 x kills"? Bug? I still managed to get the hard badge with an accuracy of >100% (and only 1% live left, lucky me) = 10010 points though. I'm playing it on a Gentoo-Linux-system (32bit) in Firefox.
It's a bit annoying that you explode when you move back into a place which is 'occupied' by a moving boulder. AFAIR BoulderDash simply does not allow to move there and only kills you if you are already standing on a square where a moving boulder drops onto.
Day 5: Start with a row of FlareGuns not too far in the front with one square between each. Remember to direct the view of the outer FGs a bit to the center so you do not 'waste view-range'. Next put 3 FuelThrowers 2 rows before them: 2 at the left-/rightmost borders one in the middle. Then 3 Flamethrowers two rows before these to block/attract the hunters. Position 2 of them 5 squares from the side and one in the middle (be precise). Set up another row of FGs one row before the other FGs (diagonal to them). Add two more FuelThrowers between the others and fill the rest of that row with FGs. Add Imploders directly behind the last row of FGs and adjust their view-range that each of them covers two FlameThrowers (I think i had 6 or 8 of them). Right before the last wave you should have money left for two BeamCutters. I put them in the backrow left-/rightmost. I only used one repulsor-skill in the first MassAttack and skill 4,3 and 1 in the last level as money is no problem then.
Although i slightly dislike these story twists where you get fooled and have been "oh so blind to serve the evil side", i still like this game very much. I mean ... first i trust a voice from an altar and then i trust a voice from a chest ... That doesn't make me see how i should made the right choice. It just makes me lose trust in anything/anyone. But maybe that's something to learn too: There is no good or bad way, just this or that way.
Mars in 2 days. Snapshot103s tactic is good. However i modified it a little, as IMHO you do not need rocket-upgrades: I used one point each on heigth, width, band and fuel on first day. Then i had a very lucky run with 2,500$. Dont get demotivated. It's all about luck. On 2nd day i spend the money on scannerX2, fuelX7, fuelsuckerX2 and the rest on launcher-stats. That was enough to make it to Mars. - Oh and before i made it to height 100.000 in freemode @day3 before i realised that i probably have to play story-mode to get the badge. Stupid me. ;)
After a VERY long while enemies stop coming in. Try it with level 1 on normal if you want to. That should take the smallest amount of time. I wanted to sit out level 13 (black imps), but lost patience after ...uhm ... maybe 2 hours. I finished the level by crushing the castle with shield-spell and got 2.384.900 loot (+90k as total). But i do not recommend this way of making money.
This simply doesn't work. You can not find the solution with logic as there are far more reasonable combinations than the author thought about and some existing combinations are somewhat wrong. Because of this the game is just about trial and error or finding the solution on the net.
@DerStupid, i did all in the first go in expert. My tactic with every stat maxed: Build 2 SuperTowers in some distance to each other, upgrade one of them, you should be left with 1250 credits. Now call all waves in one go and start bombing where the road bends (to hit more in one blow). Do not shoot too fast (you'd waste money), neither too slow and when ever you have the money, upgrade the towers.