What kind of game is this
Thirteen gears sit meshed together on a round board. Stack two characters of the same level and they evolve one step up. The blades on the outer gears reach the track the assignments travel on, and cut down whatever they touch. The assignments come as one unbroken line, and the moment a single one reaches your base, the run is over.
Grow, or defend
One slot on the board is the spawn gear. Blades that mesh with it grind it down, and when it breaks a new ally appears. The same blade can therefore be spent on stopping assignments or on producing allies. How you split them is the whole tactic. The spawn gear sits somewhere different every stage, so you rebuild the board each time.
The last choice
Only when you stack two level-4 characters does a choice appear. All-nighter (attack ×10, 50% chance, drop to level 1 on failure) or plan ahead (×5, guaranteed). You are betting two level-4 characters, so missing it late in a stage usually ends the run.