How to get past level 30 on Teeter (Android)

The main key to hexdefense (in easy or hard mode) is upgrading towers - I don't usually do hard mode but I saw your question and tried Pinball in hard mode to try it out... I got past wave 20 with only 4 towers by upgrading: The strategy I used was to put lazers in a way to maximize damage where creeps go and to use missles (red) to take remaining hits.

• I first put a lazer just above the eastern + to catch creeps on their way up (it is helpful to first note their pattern without any towers).
• Then I put a missle as soon as I could N, N, NW of the exit to take care of 1 or 2 stragglers on wave 2.
• Then I upgraded both of these fully.
• Then I put a missle SE, SE, NE of western + to maximize the lazer's damage.
• After upgrading that, I put a second lazer S, SE, SE of the western + to double the lazer damage on the diagonal between the two lazers and upgraded (both these upgraded lazers were able to take out the fire boss on wave 15).
• Then I put a few more missles in, not impeding creeps current path.

This got me to wave 24 (which is very horrible since I know people have done FARRRR better - leaderboard shows wave 117, prolly on easy mode), but this is just one strategy to work with, though I still don't know how people get to wave 260 on the Intestines level, or even to wave 50.

I don't think this is the only criteria, but completing levels in under twenty days seems to work every time.