Caged Knights are exactly what I want(wiki link): https://media3.spiralknights.com/wiki-images/2/2d/Exploration-Caged_Knig...
Just call it an apprentice or something. We got Battle Sprites because of the large amount of suggestions but they're basically equipment/material+crown sinks and the delay when using their skills hurts my DPS. Anyways!

Why Apprentices would be a good idea/How I envision it:
- Customization from Apprentices brings Grey Havens more money. Apprentices have the same level of customization as players, and equipment/costumes and can be shared with them. Costume and accessory purchases would noticeably increase.
- Preferably late game content as you'd be buying equipment, again, for your Apprentice. Players would get Apprentices after they themselves have gotten 4* equipment at least. However, I could imagine giving them to players earlier to help out new players when starting the game. We need all the new players we can get. New players seem to have trouble finding groups cause there aren't a ton of other new players and high rank players aren't always available or willing(cause we're busy) to help them.
- Same AI as Caged Knights/Intro NPCs. To an extent, the basic AI is already programmed into the game and could be shipped as is. They would just require a set of interfaces(their own health bar below players?), missions to perform with players, and a basic set of 3~ commands(Follow, Defend/Stay at this location etc..) And if they take enough damage, they'll just sit down for a bit and get up on their own eventually.
- Access to a new set of missions to be done with Apprentices. These missions could include new maps like Starlight Cradle. I would expect the same amount of missions as Battle Sprites, 1st would be an introduction, everything in between could be random levels, 5th and final mission is when you'd be given your Apprentice by Lieutenant Feron, and your Apprentice would start off with a cobalt set after completing all of those missions. Anything else could be expanded upon and improved overtime.
- Apprentices would deal 75% reduce damage when compared with players as a trade-off for their 75% increased health and/or defenses.

Summary:
- It would pay for itself.
- Apprentice Costume Bundles/Boxes.
- More late game content in the form of missions. Opens doors for lore update if Grey Havens is willing.
- Another crown sink. Buy buy buy.
- A few big spenders would buy a copy of all their costumes/equipment to look like twins with their Apprentice.
- Now there is a reason for the Shadow Lair buff.