ARPG League Mechanics provide a way for developers to add replayability to their game without needing to significantly alter existing levels or add new ones. I've made a list of some ARPG mechanics, some ideas I've thought of, and some ideas that I've seen in other games that I think could be introduced into Spiral Knights with (mostly) a low-ish development effort. These can be randomly found in the Arcade.

Potentially reintroduce gate construction where they can be generated on demand by crafting (single use) gate maps that span a tier or stratum. Players would then be able to trade/auction maps (or at least map crafting materials).

ARPG Mechanics

• Breach : Interactable objects are found randomly in the clockworks, spawning a large group of monsters when touched. Must be defeated within a time limit for a reward.
• Ritual : Altars are found randomly in rooms. Once monsters around an altar are slain, the altar can be interacted with to respawn them. Subsequent altars activated in the same depth will also respawn all monsters fought at previous altars.
• Rogue Exiles : Rarely, a maddened enemy knight may be found. They look like a player and use player items.
• Ultimatum : Choose a difficulty modifier to add to a depth. Once the depth is completed, you can either add another difficulty modifier and continue down, or you can leave and take your rewards. If you die, all rewards are lost.
• Danger Zones (Terror Zones) : A depth's difficulty is of a higher tier/depth. Levels are clearly identified on the gate map/previous elevator. Monsters and boxes drop more/better loot.
• Delve : Follow a mine cart through the level. Fill the mine cart up with minerals while protecting it from thieving monsters. Leave the depth with all of the minerals inside of the mine cart. (Would only be interesting if gate construction or another use for minerals was also added).

Clockwork Malfunctions

• Labyrinth : A larger level with multiple exit elevators and branching paths. Each elevator leads to each of the possible levels in the next depth's rotation, effectively letting you choose which level you go to next.
• Misalignment : The exit elevator is very close to the entrance. The level has multiple monster families and/or statuses. There can be conflicting resistances/weaknesses (ie Beast + Slime). More treasure boxes/monsters.
• Escape : The depth is breaking down. There is a time limit, and you will likely have to skip monsters and/or manage your health to run through traps. More treasure boxes/increased monster drops.

Objectives

• Bounties : Pick of a contract from a bounty board in Haven to kill a specific empowered enemy in the Arcade for a reward. The gate and depth is known.
• Heist : A precious item was lost/stolen. Find it and take it to the elevator without it getting destroyed (taking X number of hits) for a reward. The gate and depth is known.
• Rescue : A knight/researcher is trapped in the clockworks. Find them and lead them to the elevator, protecting them along the way. The gate and stratum is known.