Place towers along a zig-zag path to stop the invading waves before any of them reach the bottom.
Enemies march down a zig-zag road from IN to END. Tap a green cell off the road to build a tower: the first costs 50 coins, and every tower already built adds 25 to the next price (shown next to ⌂ at the top). You can build between waves too — tap a green cell you can afford to build, or tap the road to send the next wave.
Towers fire automatically at the nearest enemy within about 2.4 cells. Each kill earns 10 coins and 10 points; clearing wave N adds a bonus of 50×N coins and points. Every wave brings one more enemy, and until about wave 30 they also arrive closer together and move faster, while their health keeps rising. From wave 11 their health also compounds by about 3% per wave, so no defence holds forever. You have 5 lives — each enemy that reaches END costs one, and the siege ends at zero.
Build where the road folds back on itself. The green cells sandwiched between two parallel stretches of road — the row between the first two horizontal runs, and the pockets inside each bend — reach 8 to 11 road cells within range, while edge cells reach 3 to 5 and the bottom-right corner reaches none. One tower in a pocket does the work of two or three on the rim.
Placement beats count, because prices climb. Every tower costs 25 coins more than the one before it, so the 20th costs 525 and the 40th costs 1,025. Late in a run you can afford only one tower every wave or two, and a cheap early tower on a weak cell wastes that slot for good.
Use the pause before each wave. You can build before wave 1 and between waves: the 150 starting coins buy two towers before the first enemy appears. Tapping the road (or a cell you can't afford yet) starts the wave, so check the price beside ⌂ first.
Expect a wall. From wave 11 enemy health grows by about 3% per wave on top of the normal increase, and the extra compounds. In our simulation even a board filled with all 80 towers from the start fell at wave 44, while filling the best cells first reached about wave 41 and filling from the bottom up about wave 36. The score is 10 per kill plus 50×N for clearing wave N, so every late wave is worth more than the one before — holding out for one more wave is where scores pull apart.