Shutshimi: Seriously Swole is an updated version of Shutshimi. It's a randomized shoot 'em up game starring an armed goldfish, where every level only lasts the ten seconds of a goldfish's memory.
After each level you get the shop screen, where you have a few seconds to select one of three "upgrades" - ranging from alternate weapons, shields and options to slowdowns, inverted cameras or controls and items which replace the enemies with flying butts. Some upgrades, such as weapons and hats, last forever or until you lose them, while most last only a single level. You have to choose an upgrade, even if all are unwanted.
Every five levels you're faced with a boss fight. If the timer runs out before the boss is defeated it runs away, but you'll face it again after the next five waves with its health bar where you left it.
In addition to the arcade mode with three difficulties there is also a boss rush mode.