While building his own shmup, Michael Molinari spent years reverse-engineering why commercial shoot-em-ups feel fair and why so many free and indie ones don’t. The result is a checklist for scrolling and arena shooters, and nearly every rule reduces to one idea: the player must always be able to read what is dangerous, what is hittable, and what is coming.
The rules that matter most:
- Enemy bullets must always be visible — on top of explosions, pickups, and enemies. Hidden bullets mean unearned deaths, and the only sanctioned hiding place is the HUD.
- Off-screen enemies shouldn’t shoot, and bosses must be telegraphed — a warning, a siren, or a lull in enemies so the stakes register before the fight.
- Bullet collision should be accurate, and a small hitbox must be visibly obvious — players need their sweet spot readable in the few frames they have.
- High bullet/background contrast — Cave’s signature pink-and-blue bullet palette is a deliberate legibility choice.
- Hit feedback is non-negotiable: enemies flicker or spark when shot, everything destroyed explodes, and boss explosions should be a spectacle.
- Levels need flow — structure that forces you to zig and zag, with “popcorn” enemies filling the gaps and making the player feel powerful.
- There is always a way out — a bomb or invincibility move, and bullet patterns designed so an escape route exists (the craft known as bullet herding).
- Camera shake is a privilege, not a right — overuse adds noise and dulls the effect.
Molinari closes by naming free shmups that get it right — Arcanacra, Cube Colossus, Death vs. Monstars, Heavy Weapons — so the checklist reads as observed practice, not armchair theory. His final warning is the most transferable: even a single out-of-place sound effect can ruin the whole experience.