The "Empty Mob Spawner" is a mob spawner that does nothing at the moment. How is that good? Well, you will see what it does. Try right clicking it. It will open up a gui. You can place a mob egg in an empty slot and click the activate button. Your empty mob spawner has turned into a spawner temporarily. The empty mob spawner will obtain 100 spawns per egg. then it will reset after those. You can add the spawns up until 1000 spawns. Here is the picture of what the gui could look like:

Example: If you put a zombie egg in the empty mob spawner, it will consume it and make zombies spawn 100 times.
There is a way to set the speed of the spawner. There is a button below the slot, that adjusts the speed of the spawner. You can set it to slow, normal (set by default), or fast.
The empty mob spawner can also be placed next to other spawners, but not other empty mob spawners, making a way to power up grinders.
How do you get this amazing block? You will have to use 750 credits in the shop or via special offer.
If any new block was added to Craftland, this is what I would want.
I hope you enjoyed this suggestion!

~camyoshi