The item would be a shadowy bomb that allows the knight to store and move monsters around. The bomb would have the same charge time, radius and damage as the heavy deconstructor, with the movement speed penalty and detonation time of of big angry bomb.
When the bomb explodes, non-giant/boss/player mobs within it vanish in the explosion to "another dimension", aka some random coordinates on the map or what have you (so as to not break the game and trigger waves). The bomb stays on the ground afterwards, twitching until a minute or so later, when it explodes open and the mobs return. If the knight drops a second bomb while the first is on the ground, the bomb explodes outwards and frees the previously "captured" monsters. All instances of the bomb on a map work as one and the same; if Skepticraven traps 4 enemies in a bomb and I place one afterwards, I will release them.
The bomb can vanish a certain number of enemies, depending on their size, after weighting all of the enemies within it. For instance, a lumber might count as 3, a trojan as 5, a zombie/gremlin as 1, Vanaduke as 30 and a glop drop as 1/3. The 3* bomb would be able to hold a total of 1, the 4* would be able to hold a total of 3, and the 5* would be able to hold a total of 5. Most enemies would be considered as "one", but it would be best to treat larger/smaller enemies correctly. If the bomb is used on too many targets, it would take the first enemy it finds first, adding toghether in whichever way until it can fit no more. Excess enemies are jerked towards the center, and take extra damage.
The bomb would be relatively worthless in lockdown, as it can not vanish other knights. However, since the bomb cannot abduct them into an alternate universe, it would do the extra damage and might be of some use when used creatively.
@"The Bomb is OP"
I think that bombers could use some new interesting support items like this, especially ones that are strong. It might seem too strong at first, but at the same time it can only vanish 5 normal sized mobs if you get all of them and requires you to walk very slowly while placing it carefully. In a lot of situations, the bomb would not be so practical. In a lot of other situations, the bomb could be used to handle things perfectly.
But mostly, it isn't supposed to be the most practical weapon in every situation. Just the coolest.
Really interesting. I like it.