Swarmers. I've always thought they've been really cool in ways ranging from their "lore" to their language of music notes. There's some swarmer oriented stuff in the code too, lying dormant from event to event. Anyways, upon becoming one you get the message:
Spoiler:
Anyways, I think it'd be awesome game mode if first swarmers come, followed by their true masters. I think the type of game mode would be centered around domination/summon type. Effectively, the stronger the swarmers get, the more powerful beings come through the gateway. Possibly swarmers can "upgrade" to said beings via materials intaken, like a mild form of shadowling ascension. Effectively, the goal of the swarmers and their upgraded selves is to set up a beacon, and then signal their ancient masters to come and find them.
There's a lot of potential here, just typing this I can think of numerous awesome ideas and parts that could be added to this game mode. Naturally, it would be the baby of the code if they choose to take it.
Again, this is very rudimentary and the roughest of drafts. I'll throw on some of my own ideas to get the ball rolling.