(This was originally posted in a dead thread - a friend suggested I move it over here. I know some of this has been suggested before, but I think I'm posing it in a unique way. Apologies if I'm wrong on this point.)

It's fairly obvious, and has been stated often, that an end-game crown sink is necessary, as there is a constant influx of crowns from players dungeon diving, and yet once a player has all the gear (s)he needs there is nothing left to spend it on. The result is that crowns continue to proliferate, and with increased supply comes lowered demand, leading to continuous inflation. OOO understands these basic economic rules, as mineral boosting was intended to be this end game crown sink, allowing players to spend their big ol stores of otherwise useless crowns on influencing gate construction. It would have been a self-sustaining sink, as well, as gates cycle out regularly. Unfortunately, the drive for people to do this wasn't that high, costs were astronomical, and the mechanic had some serious flaws. So the question becomes one of what to replace mineral boosting with. It has to be something repeatable that costs a significant (but not obscene) amount of crowns, and there have to be incentives that are capable of sustaining the system either indefinitely or for a good deal of time (and if the latter, new incentives have to be easily created and implemented in order to extend the crown sink).

Enter the neverending dungeon.

Message from Spiral Knight HQ: "Surface Excavation Squad Sigma has recently uncovered a strange ruins not far from Haven. Exuding an unsettling aura of energy, this ancient gate opens into a dangerous section of the clockworks that seems to defy physics and go on forever. Spoken of in hushed whispers as the 'Eternity Well' by Haven citizenry, its original purpose is unknown, and a guard has been posted at its entrance due to the exceedingly high risk to life and limb the area poses to unsuspecting and inexperienced recruits. The guard has been known to turn a blind eye to his duties for the right price, however, and some bold knights are treating the impossible place as a challenge by which to prove their valor, vying to delve deeper and dispatch more foes than their peers. In fact, the Loose Cannon Adventure Society has set up shop nearby, promising fabulous prizes to those who can bring them tokens of their success from the endless depths. This group seems to be all about appearances though..."

Basically, the neverending dungeon would be a series of randomly themed strata, 5 levels apiece, punctuated by rest points at which players are rewarded tokens (Infinitus Sparks or Mobius Emblems maybe; more on this later) and have a chance to swap their gear. Monsters begin at tier 3 strength and gradually get stronger with each level. Eventually their stats become so great that defeat is inevitable - the challenge lies in how far you and your team can get. The first 4 levels of an Eternity stratum would be normal stages, and the fifth would be a challenge just before the rest point. These challenges could be anything: an arena, a timed "eliminate all monsters" challenge, or a boss (either scaled up versions of existing bosses, taking on two of said bosses at once, or unique boss variants like a poisonous Jelly King). Additional wrinkles could also be added to ensure added difficulty: guardian specters like the phantoms, inability to revive, time limits, etc. Elevators are free, but players do not gain any crowns or materials in the dungeon. Paying the guard at the entrance affords players one attempt. This price would probably be somewhere between 10 and 25k crowns - not enough to be prohibitive to those playing on mist, but enough so that the easiest way to finance such runs would be selling CE. (For those worried about extending amounts of gameplay beyond what OOO intended, remember that you can purchase 100CE for much less than this, even now. Plus, the brutal difficulty ensures that gameplay is far from literally neverending, and provides Ian with an outlet for his sadistic developer inclinations. <3)

The rewards for the unending dungeon would be twofold: the first would be leaderboards that display individual names and guild affiliations of those who progressed the furthest in the dungeons. There may have to be some sort of point system implemented here to differentiate between similar results, and between those who were killing everything and those who just ran through. Awarding points in place of crowns for dispatching enemies and a bonus for making good time should work. There could also be a "press your luck" element in which you only get the full points if you ascend via elevator - dying subtracts a penalty from your final score. This would encourage competition between the highest level guilds and players, something most other MMO's have (such as racing to beat new content or PvP), and for a reason: personal glory and competition are self-sustaining rewards that keep people playing.

The second reward would be the prizes that the dungeon tokens are exchanged for (1 token is found at the first rest point, 2 at the second, and so on to better reward skillful attempts). These prizes would be largely aesthetic, as the neverending dungeon is intended to be a bonus challenge operating outside the "main" game: armor and helm costumes, familiars / pets that follow your character around Haven, paint that reassigns your primary color, silly trinkets that do fun non-combat things, etc. If Team Fortress 2 hat lust has taught us anything, it's that people can and will go nuts over personalization items, even if they have no effect on gameplay. These items do not provide neverending incentives for people to spend crowns trying to get, but they are easy to design and to implement, and so new ones can be released on a fairly regular basis without much trouble.

Finally, this content would have the additional benefit of encouraging a wider variety of gear (players without shadow gear would likely get mauled in a > T3 fiend or shadow stratum, for example), and so would extend the life of the current crafting game (another, though very limited, crown sink). Along with the costume rewards, this would also ameliorate the problem of most tier 3 equipped players wearing the same thing. Above all it would be a fun and unique endgame challenge, and because it reuses content from existing levels shouldn't take a large amount of developing power to implement and upkeep. And besides, who doesn't want a pet snipe? :)

EDIT: Changed title for accuracy.