okay then, long explantation time:
There are 5 ways to make your pokemon's Shadow meter go down, and the effectiveness of each varies, depending on the pokemon. the methods are:
Make it battle: kinda obvious here
Call it back form Hyper mode: when the pokemon entered Hyper mode, hit the Call button.
Use colone scents: these can be bought at the Agate pokemart, but you need the Colone Case first
Walk around with it: nuff said
Leave it at the daycare: can anyone say EXPENSIVE? but this is lasy-mans method. but you have to cough up lotsa cash.
The perconality of each pokemon chages how the methods work. for example, one can make batteling deplete the meter quickly, while another will have it so that battleing does virtually nothing to the meter.