Shutshimi

Shütshimi is a randomized shoot'em up about a muscle-bound fish with memory problems defending the seven seas.
Armed with your trusty bullet-morphing shotgun, defeat or navigate through waves of enemies and collect powerups as you battle your way through each of the game's bosses. But there's a catch (there's always a catch): you've been cursed with an incredibly short attention span. Combat waves and upgrade cycles only last 10 seconds a piece, so you'd better act fast!
But wait, there's more (information)!
Fishy Features:

• Endless waves, endless fun!
  
• Rapid-fire gameplay! The rules change every 10 seconds, so react quickly!
  
• 5 different weapons to choose from!
  
• Over 40 upgrades to acquire! Combine upgrades with different weapons for interesting combinations!
  
• Hats! Over 30 of them! Most hats unlock hidden "Hattributes" which modify gameplay even further!
  
• Full keyboard and controller support! Play any way you like, as long as it's either of these two options!
  
• You can smoke underwater!?
  
• Leaderboards! Compete with friends and foes for the global top score!
  
• Local Co-op! Work together or screw each other over when competing for the top score