Gone are the Pokémon Centers, Shops and Gyms. Gone are the houses, villagers and friendly Professors with angry nephews. It's just you and 386 wild Pokémon. And you're pretty sure someone out there wants you very, very dead.
'Cause y'know, it really wasn't hard enough already...
Wild Pokémon's levels are calculated with the formula "level= random(X)-random(Y)+Z" Where X and Y are map-related variables, and Z is the weighted average of the Player's current party.
Easy: The formula is modified so that X=0 - thus the levels of all wild encounters will be lower than the weighted average of the Player's party.
Normal: The formula is unchanged.
Hard: The formula is altered to double the value of X, resulting in higher levels. Encounters are 10 times as likely to happen in grass and in caves. Saving in the field is disabled (autosaves only).
Autosave: This feature saves the game at specific intervals: sleeping in bed, winning certain Event Encounters, entering a new region or dungeon, etc. Turning it off on Hard Mode will mean that if you lose the game (when your party is defeated and your health is "critical") you must start a new game.
Nuzlocke Mode enforces the second rule of the popular Nuzlocke Challenge: When a Pokémon faints, it is removed from the party. This includes poisoning in the field as well as during battles, but the removal won't happen until the battle is over. It's up to the Player to enforce the first rule.
These features are all currently implemented and functional in the game. So, video soon!