Inferno

Inferno is the name of the newest difficulty level in Diablo III.

This difficulty level is tuned to maximum level players (level 60), and every monster in Inferno will have an mlvl of 61 to make a flat increase in damage across the whole of the difficulty.

Inferno was also a fire spell in Diablo I and Diablo II. It worked like a short-range flamethrower, dealing fire damage to anything in range for as long as the skill was activated. Inferno is not present as a Wizard skill in Diablo III.

The spell type has become so well known through Diablo and other games that other spells with a similar range/effect are often referred to as "inferno-like" spells.

Design Intentions

The intention for Inferno is to add a level of play to the end game of Diablo III that does not involve monotonous boss runs, or what Blizzard calls "the path of least resistance" to grow a character.

Bashiok commented on the issue of Inferno and end game after it's Gamescom 2011 reveal on the battle.net forums[1]:

The general philosophy [of end game] is that we want to make finding better loot at the end game more enjoyable, and attempt to address 'path of least resistance' style gameplay.

There's a couple ways we're doing that, some of which we're not talking about just yet.

Primarily it's focused around Inferno and creating a consistent difficulty across the entire act. By having a flat difficulty across the entire game in Inferno it evens things out so that no matter where you want to go you're being challenged, and you have a good chance at getting good drops. That's intended to open the game up so there's simply more freedom for the player to go anywhere in the game and have an equal chance at good drops.

There will probably still be a slight difficulty curve in Inferno, as enemies simply become more complex and have greater abilities later in the game, but we're making an effort to make it as even across the board as possible. It's something we'll very likely have to keep tweaking after release.

In addition we're attempting to de-emphasize path of least resistance by creating a more equal value across monster types. We're not going to get into specifics about who can drop what or how much, but our intent is that being out in the world exploring should be as lucrative (potentially more) as simply aiming for the quickest-to-reach boss and running that over and over.

Getting people out into the world of the game and away from repetitive boss runs is essentially our goal. It's going to be tough because people will find a path of least resistance, and they will make that the game. We're going to have to keep on top of it, and truthfully it's something we're still working on. We'll likely want to have some additional features to support these ideals, but just getting Inferno tuned right is our current end-game goal for ship.

And also later followed up this initial post with a few other elaborations:

I don't think it's ultimately what we want for the end game either, but it's a great start, and we think plenty to keep people engaged for the initial release.

[...]

If we believe it will make their play experience more enjoyable or rewarding, absolutely.

The problem is people do boss runs over, and over, and over, for years, and it's not because the boss run is fun, it's because it's the path of least resistance to finding an awesome item. No one wants to do repetitive boss runs.

If we can instead say the path of least resistance is the entire game, that there's no single boss you have to repetitively farm to get the most items per hour, then the game is better for it and the players are liberated. They now have options to go anywhere they want to look for items. Hitting that perfect balance is probably near impossible, but we think we can get pretty close.