Mob grinders are not allowed anymore.
This is due to exploits.
There are some exceptions:

1. There is no water inside the spawner space.
2. The mob's health is not reduced by an automated process. Eg: drowning, suffocating, dropping, burning or cactus.
3. The Mob is killed by a player not a automated process.
4. The mobs can move freely
5. The mob's path to the player must not be obstructed.
   Players found to be abusing this will have the Mob SPAWNER removed.

We also have a new capture event!

Bonus Prize: 2 master balls randomly drawn throughout the first 5 winners. Post your entry here
Have a great day!