You know the cages with captured knights in some missions, right? You would use this kind of cages as decorations, but with monsters such as (all kinds of) zombies, gremlins, jellies, chromalisks, and lumbers. These cages would be as tall as normal guild hall walls, and would have similar texture to the mission cage. Jelly cubes and gremlins in these cages could be interacted with, the gremlin saying "King Tinkinzar will free me and destroy you little fools!" and the jelly saying "You will be absorbed by our Queen... Hahaha. Haha."
To make a cage for a specific monster, you would need to kill the monster you wish to kidnap. You would have 10% chance of getting a special material needed to craft the cage with the monster.
About the gremlins, you can only capture thwackers.
The material names and descriptions are:
Gremlin: Gremlin Thwackhammer
Desc: A thwackhammer used by Gremlin Thwackers. It often makes sounds of engines.
Jelly cube: Jelly's Jelly
Desc: A piece of jelly that Jelly Cubes are made of. Some knights use it as soap.
Lumber: Lumber Gear
Desc: A huge gear that is a required piece for Gremlins to build a lumber. Some are too heavy to pick up.
The cages could be crafted in the hunter lodge alchemy machine.
Why not, on a chance interacting with a monster, that the monster will hold you hostage until two "Guild Prison Guards" break up the commotion.? If they fail (another on chance) you are "Defeated" until one of the prison guards revives you.
Hmm, if only I could expand this.