Water only world v0.1

Survive in an endless ocean no land no structure 

Obsidian: Only way to get obsidian is to buy Pointed Dripstone from wandering traders (to make lava generators). I'm not sure if wandering traders spawn in this world

Iron: Best option is to make an Iron Farm since mining is restricted 

Ender Pearls & Blaze Rods: Found only by venturing into the Nether (so you need obsidian for a portal).