Perhaps the hard badge wording should read 'Reach 7km without totally losing control of what you're doing because nothing responds to commands and the game keep jumping around like an epileptic on a trampoline'.
I did the 18th from the right side of the screen - started 1 collector and 1 blaster, added collectors where they fitted, then a mortar which I flew around a little bit to wherever was needed while adding a few reactors, an extra blaster, then a drone. Drone to keep levels down to ease pressure on blasters, couple more reactors, more blasters, and from there it's easy enough to finish.
September 18th is a thing of beauty, probably the best map the game has ever produced. Only one I've ever wanted to keep, anyway... Did it without the blaster trick, building up from a tiny enclave on the right of the screen.
This game could do with a big clear link to the Creeper World Training Sim. This edition is more for people who already know how to play the game - so if you're struggling, try the Training Sim first. Or use the pause button (building while paused is a huge advantage) and move the city (starting position is rarely optimal) options more.
Torsomi: 10th is indeed on the hard side, but doable. My (casual, perhaps not for experienced speed-players) method was to move the city down a bit into the little 'bay' directly below it, use one blaster to stop the creeper coming in through the low channel, and two above the city to keep it safe when the creeper reaches there. From there build up with reactors on the high ground with a mortar or two to help keep the creeper down. Should be easy from there.
If you're struggling, try Creeper World Training Sim (by the same developer). Some maps on here can be tough if you're not entirely sure what you're doing.
I might be missing something (I rarely turn my speakers on) but there's a sound on/off icon in the control panel on each mission. One for music, one for FX.
On 45, build up what barracks you can then just launch everything you have at the big blob. Might take a few tries, but eventually you'll capture it and it's easy from then.
I've never really gone for speed, except a few times on the full game's custom maps and stuff when there was a bit of a leaderboard battle. This is just my daily 10-minute (ish) thing I do casually - still probably quite fast at it, but I'm more concerned with making sure my builds are neat and symmetrical than I am with being cutting-edge quick.
It got lots of minus votes because commenting about Minecraft creeper on the comments of this game is pretty much a guaranteed -10. Assuming that's the 'green creeper' you referred to.
If your save file has gone, it's because you deleted it (almost certainly accidentally). They're stored locally on your machine, and unless you take care they can be deleted by clearing your broswer history, using CCleaner, things like that. http://www.kongregate.com/pages/help#savesmissing
Found the hard to actually be rather hard (no premium). Flying Castle level was the hardest to 3-star, I thought... overall the one thing that irked me the most was the fact the hero just froze when you tried to move him from one giant to another. Just hung on, doing nothing, until it died. If you expect people to buy premium, at least make the basics of the game work properly.
 "Road of the Dead 2")
 "Cyber Chaser")
 "Zombotron 2: Time Machine")
 "Creeper World: Evermore")
 "Real Men Wear Pink")
 "The Bravest Hunter")
 "JellyGo!")
 "Papa Louie 2: When Burgers Attack!")
 "Coaster Racer 3")
 "Giants and Dwarves TD")
fair enough