Even the best twin-stick shooters on mobile lower the difficulty to compensate. Isaac offers no such mercy. If you die on Depths II because your thumb slipped off the "fire" button, you lose a 45-minute run. That frustration is why most commercial mobile ports have failed.

The most significant technical hurdle was the control scheme. The Binding of Isaac requires dual-stick shooting: one thumb moves Isaac, the other fires tears in a direction independent of movement.