...yeah. Like the title said. When you run out of energy, it's usually time to log off Spiral Knights, and, in my case, twiddle my thumbs waiting for more energy to regenerate.

So what if there was a sort of challenge gate? You could go in there by paying a fee, PvP style. Once you're inside, all elevator costs are free, but the only things that monsters drop are health, pickups, and crowns. No heat or tokens at all. The crowns aren't actually earned, but they do increase your score. All treasure boxes will hold some sort of pickup.

There will be a single player challenge mode, and a multiplayer one, where you can create a party of up to 4 before you start the challenge. It will also be split into tiers, with your equipment downgraded to the proper tier. You can only do a tier's challenge if you gain clearance for that tier. The costs per tier are:
Tier 1 Challenge: 50 crowns
Tier 2 Challenge: 200 crowns
Tier 3 Challenge: 500 crowns

The whole point of the challenge is to get the most points possible. When you die, the challenge is finished and you get sent back to Haven with rewards based on your score and what tier you went into.

The levels are random, and the gate map is created as you go along. The elevator to the next floor always displays the "?" that appears on an elevator to a Treasure Vault/Graveyard level. However, every 10 levels or so, there will be a predetermined level set, such as Concrete Jungle, Dark City, Gloaming Wildwoods, a full 3 floors of Scarlet Fortress, etc. These levels can appear out of their proper tier, and will be adjusted for difficulty accordingly. (Tier 3 Snarbolax! Tier 1 Royal Jelly! General craziness! Not Vanaduke, though. He's Tier 3 only.) Your equipment power stays the same for the whole challenge, along with enemy power, being Stratum 1 power if 0 star, Stratum 4 power if 3 star, etc.

Rewards... well I don't have a clear idea in mind. There's definitely a leaderboard, and maybe random materials would be given out based on how deep you managed to go. Tokens, too, perhaps.

Scoring totals would be separated like this:
Depth Reached
Crowns/Minerals Collected
Monsters Killed
Level Sets Reached

Since the new missions update, there's more backstory to the game, and enough for me to spin a bit of it into a backstory for this challenge. If it sucks to you guys, you can think of a better story, because my storytelling skills are more subpar than a pro golfer (rimshot):
The depths of the Clockworks have been cleanly organized since the crash of the Skylark. However, this may be because of where the entrances to the Clockworks are. The Spiral Order has started excavating a new gate, and needs the help of the Spiral Knights to chart it. Due to the continued interest of such an idea, the Spiral Order has agreed to sponsor the energy cost of descending in exchange for the materials, crowns, and heat acquired. Descend into the new gate, and see where it leads!

Of course, I have terrible balancing skills, so feel free to add on corrections that I could make to this idea so it actually makes sense. I'll probably add on most of your ideas, because this is just barely thought out. I'm just throwing it out there.