speculation time! so far I have noticed: keys needed to unlock chests (keys in his inventory), a larger variety of underwater animals, underwater caves and rock formations, mega sharks, a strange laser beam coming in from above (despite both players presumably wielding a weapon unrelated to it),potions can be placed (on the crafting bench), much more variants of coral, super sharks, a strange underwater background (possibly still the regular floating island background),the player who made the screen shot is "Mrs biome" due to the fact the drowning logo is in the players inventory, wings don't seem to work underwater (otherwise the players would be using the ones the have equipped instead of a grapple hook), and finally: levelling up is not limited to weapons. most likely this will be our new method of increasing health, mana and overall power.