1. Get CO Loader.
2. Open CO with CO Loader.
3. Enter the Halloween Map.
4. If your server is like mine, then there should be a whole lot of people swarming around where the DarkDemon spawns. When the mets drop, everyone is standing on them.
5. Press 'hide' the people should dissappear, but the items should stay for a few seconds. (This is what happens on mine)
6. Quickly grab the mets.
7. Repeat.
I've been doing this for the last 2 hours, and have collected over 40 mets.