Press the left & right arrow keys to move Copper Fish. Press up to jump. You can use this to dodge enemy fishes or aim higher. Press the space key to spit oxidized copper. Defeat all 100 fish to win.
Credit to @-gge, @potatophant, @excelguru & myself for knocking a bunch of unrelated people down this giant rabbit hole that we call the Mineral Fish fandom. The music appears to be from a Paper Mario game. Credit to @Bubbles166 for finding it. Thanks to @-gge for making the E Simulator games, and @Copper_Fish for turning them into the Copper Fish Simulator games & inspiring me to make this.