AKA: "A thinly hidden attempt to bring back the content thrown away in events"

I've made several comments about this before, but never bothered to make a full-fledged thread about it.

Currently, all your choice between Normal/Hard/Elite does is deflate/inflate enemy stats/drops based on your choice. Nothing of any tangible meaning changes; it's just an artificial difficulty slider. Besides, the 'tier' system already handles enemy difficulty and loot!

Before I start, a couple things that are simple but still important: when in the Arcade, all depths are randomized and set once you start the preceding level; no more waiting it out. You can still check what your possibilities are, but you won't be able to see what the next level is until you're at the elevator. Also, rename Normal/Hard/Elite to Easy/Normal/Hard, because that's what they actually are. Lastly, normalize the loot given from enemies across all difficulties- it should only be changed according to what depth and level you're in.

Difficulty should instead have an affect on what levels you play in the Arcade. A single gate could have three "styles" of layouts, each for a different difficulty setting. You'd never see difficult level types if you're playing on Easy, and you'd never find easy sets on Hard, with Normal being the middle-ground, generally giving you 'Normal' levels with some odds of finding other difficulties now and then.

'Easy' levels have very little enemy variation, with few floor hazards, a lot of room to move, and barely any puzzles. Examples are Wolver Dens, Deconstruction Zones, and Lichenous Lairs.

'Normal' levels are a step above Easy in some way or another. They could have more hazards, more enemy types, less breathing room, some more puzzles- but not necessarily all of those. This also includes levels with "dynamic difficulty" that changes based on what you do in the level. Examples are Clockwork Tunnels, Graveyards, Dark City, and Boss Stratums.

Treasure Vaults appear very rarely in Normal and more commonly in Hard.

'Hard' levels are those kinds of levels that you don't want to go into unprepared- they've got tough enemy combinations, lots of tricks and traps, and might even be cramped. Compounds and Candlestick Keep are both good examples for this.

'Special' levels would never appear on Easy. Instead, you'd find them while playing on Normal or Hard. They'd also include levels appearing in the various "content events" that get benched for months on end. They're only accessible at the T2 and T3 Terminals. These levels have some strange gimmick, or are just ridiculously hard, and typically come in a series. They're a break from standard gameplay and have great rewards! The catch is that you need to pay a certain amount of minerals to get in, the level being chosen based on what you put in. Some 'Special' levels/series include:

[Normal + Hard Difficulties]

-Dark Matter + Valestone [Obsidian Nexus -> Fiend arenas/Fiend Clockwork Tunnel (based on difficulty choice) OR Grasping Plateau -> guaranteed Grasping Plateau]
-Valestone + Moonstone [Graveyard -> Candlestick Keep with guaranteed Black Kat fights (# and room design based on difficulty)]

[Hard Only]

-Crimsonite + Luminite [Dark City with information on Tortodrones -> 2 levels with passive Tortodrones -> 2 tortodrone fight, just like the event]
-Moonstone + Crimsonite [Mount Krampus 1 and 2, enemies drop loot too this time]
-Dark Matter + Luminite [2 random Danger Missions back to back, can't change equipment, second treasure room is much larger than normal]

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As for missions, they'd be the same as ever, but now they'd display their forecasted difficulty and won't let you change it.