I can't say this idea has not been brought up before, but what if we had some stages with large bodies of water?
How it works: In some stages large bodies of water would spawn at low elevations on the map. Knights that get completely submerged will be immediately inflicted with a status effect called (simply enough) "water". Represented by a small water droplet and by bubbles above the player's head, water lasts for 20 seconds and initially does not do anything, but when the effect wears off the player loses either 4, 8, or 12 bars (each bar being 1/4 of a hit point) of damage depending on tier (tier 3 takes the most damage). The water effect can also be removed/cured by entering air pockets (patches of constantly flowing bubbles never more than a 8-second walk from each other), using a remedy capsule, using a bubble item (which will be discussed below), or leaving the water. On a side note, water will be instantly re-inflicted if the player takes water damage or uses a remedy capsule.
Being submerged does some interesting things to the status effect system. Fire and stun do not work in water at all - fire for obvious reasons, stun because the friction from water is too great for the blow to hit hard enough. However, unlike an ignited player, a stunned player will remain stunned upon getting submerged. Ice, poison, sleep, and curse work fine (if it was real life a frozen enemy should float, but this would be nearly impossible to incorporate into spiral knights), but the real interesting changes occur with shock. Enemies (and players!) will have their shock resistance reduced by the equivalent of a "Very high!" unique variant, will take more damage from shock, will be disrupted by shock more prominently than usual, and will produce large "T"s or "X"s of electricity which WILL shock anyone and anything that gets hit. This can be a blessing and a curse to players that use shock-inflicting weapons.
Enemies defeated while in water will have a chance to drop a bubble. The bubble works similarly to a remedy capsule, except it cures only water and fire (the latter trait not usually being useful in a level with water). When used in water, the bubble item will also protect the player from receiving water again for 10 seconds.
Please comment/add on to this idea and state whether or not it is a good one.
This actually seems well thought out, and in keeping with the Spiral Knights atmosphere.
I certainly wouldn't mind this getting added.