This is more of an eventual thing, but I think it would be great if a stealth mechanic was added to the combat of LoE.
Of course, I don't know the exact current mechanics of how or why a hostile mob notices the player, but having a way to either make it so mobs don't see you, or purposefully get their attention would be great.
Now, sneak criticals and things like that would be great, and are pretty common in games, but something less common, but just as useful is a mechanic for purposefully making noises to get a creature's attention.
With all the area buffs/debuffs currently in the skills list (like Regenerative Aura and Candy Shower), and the advantages of battling with a group of friends, a main problem comes with getting the attention of mobs to get them to come to you. Creating a stealth system that allows for both sides of the spectrum would be nice.
(I'm going to assume there might be a reason LoE has obscure creatures, but not certain ones from the show, like hydras and ursas. Though if those are a possibility, that would be great, too.)