shadowbuild's March 4 challenge: Completed in 51:04, all emitters capped, no Storage, Speed, Reactor, or Drone at any time.
Would've been a lot faster if I had pushed north earlier, so I could take advantage of the huge basin it would unlock, but anyway.
My strategy: IMMEDIATELY push for the upgrade point, and put it in RANGE.
Then, push east to the high ground as fast as you can, and get a mortar set up on the eastern edge of it. The range upgrade will allow it to bomb one of the basins, and it can be put south for some quick bombing of the southern basin, allowing pushes forward and disposing of a lot of creeper. A single mortar covers the large northwest basin and is powered down most of the time, powered up when the creeper gets deep to make it stay back.
How exactly do you manage to corrupt cops into giving you a rocket boost for flattening them instead of stopping you?
You'd think the corruptible would, you know, try NOT to get killed or something.
@Rymanrocks It blatantly says right after the achievement that you must immediately try the level afterwards.
The fact that you need to is stupid, but it DOES say it RIGHT THERE.
@megamerio33: You CAN move in the grey area, actually. There's an opening into it on the right side.
You have to time the blue switch right so you can get in from the right side after hitting the red switch, and still reach the button in the center around the blue wall.
@thecerebralsloth: It says in the description for Heroic and Iron challenges the max level of upgrades you can have for that challenge. The level increases for later on maps.
Basically, if you want to do one, you should reset your skills so you don't put anything over the max level, and try to maximize what you have within the level cap. If you're doing Iron you probably shouldn't put anything in lines you can't use either. Just do note that some maps have preexisting structures of the types you can't make. If it has those, you should upgrade that line as well.
Additionally, Rangers can be used to remove Necromancers from blobs of skeletons, because if you give them Poison they'll seek to poison everything they can. This also causes them to ignore skeletons and Magma Elementals if there's anything they can poison within sight. This will cause them to completely ignore the summoned skeletons and kill the necromancer outright.
Then they'll use Wrath and clean up all the trash for you. Honestly one of the best towers.
A useful tip for challenges where you can't use artillery:
Rangers make pretty good mass trash disposal when they use Wrath of the Forest. Use them to dispose of huge swarms of guys.
It also is nice because it stops them for a while, and if you have a bunch of Rangers, you can nearly bring enemies to a halt by chaining it, while the spell and the Rangers' arrows kick their asses.
Towers should have the option of different targeting mechanisms. For instance, Mages should be able to target armored enemies over others, and try to ignore magic resistant when possible. Cannons target groups, archers shoot air or magic resist, these kinds of things.
I'd have actually tried to figure out the last 2 levels myself if I could remember all the damn teleporters. As everyone else has already said, needs more than 2 colors.
Jan 4 was cake. Go around the rim on the right, get reactors up, set up a few mortars around the basin once most of the rim is done (far more effective than blasters for holding a lower area at bay like that) and get a drone early, doing bombing runs down the gorge in the middle.
23 minutes easy.
 "Creeper World: Evermore"){kind=icon}
 "Papa's Taco Mia!"){kind=icon}
 "Burrito Bison Revenge"){kind=icon}
 "This is the Only Level 3"){kind=icon}
 "Penguinz"){kind=icon}
 "Two Rooms"){kind=icon}
 "Kingdom Rush"){kind=icon}
 "My Little Army"){kind=icon}
 "My \"Dear\" Boss"){kind=icon}
 "Blockage"){kind=icon}