A many-segmented crawler snakes down through a mushroom field — shoot a segment to split it in two and clear every piece to survive the wave.
Touch and hold anywhere on the play area to slide your shooter left/right toward your finger — while you hold, it auto-fires bullets straight up. The shooter stays on its row near the bottom. Shooting a crawler segment kills it, drops a mushroom in that cell, and splits the crawler into two pieces; the back piece reverses direction. Crawlers hitting an edge or a mushroom descend one row; past the bottom they come back up a few rows and keep weaving through the lowest rows. Shoot mushrooms (four hits) to clear paths. A wave ends only when every segment has been shot — the crawler grows by two segments a wave up to 18, and it gets faster every wave with no top speed. A segment moving into your shooter's cell costs a life; the pieces near you are then sent back to re-enter from the top. Three lives total.
Splitting near the middle pays better than the tail. Every split creates a new piece, and the front segment of each piece is a head worth 100 points instead of 10. The back piece reverses and walks away from the new mushroom, so a middle hit leaves two pieces heading in opposite directions — more points on the board, but more to track.
Don't shoot every mushroom you see. Each mushroom is also a built-in deflector that helps trap the crawler into descending. Clear only the mushrooms blocking your firing lane straight up to the head; leave the ones to the side as built-in walls.
Your shooter is locked to its row, so you can only dodge sideways. Crawlers that pass the bottom come back up a few rows and keep weaving through the lowest band, and that band is where lives are lost. Stop pieces while they are still high, and keep a clear column to slide into when one comes along your row.
Only a segment that moves into your shooter's own row and column hurts you. A crawler at row 3 can't hurt you yet, and neither can one on the row just above you until it drops. Shoot the lowest piece first, no matter how long the one higher up is. The crawler speeds up every wave with no limit — about 2 cells a second in wave 1, 6 by wave 12 and 10 by wave 20 — so every run ends; surviving longer is what pays, because the wave bonus is 100 × the wave number.