Click the enemies to damage them. There will be harder enemies that come less often (trasher = easiest and nuclear terror = hardest) Enemy spawnrate slowly goes up. The sulphurous scales are your money. The blue number is your seafood, press 1 to consume 1 and summon the aquatic scourge. The purple number is your bloodworms, press 2 to consume 1 and summon the old duke.
Credit to Terraria Calamity Mod for all the sprites, music, and biome.