3rd Gen For anyone interesting here is how to connect Pokemon Colloseum (Dolphin) with GBA Pokemon games (VBA)

This took me over a year to figure out but im content with the results. For anyone having trouble like I did here are the steps i followed to make it work:

1.Open VBA-M and set Link type to Gamecube

2.Keep VBA running and open dolphin

3.On the controllers, set the second controller to GBA and also check the "Allow background input" box

4.On the VBA, make sure you have unchecked the "Pause When Inactive" option and now, hit "Start Network Link" as a client

5.Open Pokemon Colloseum and go to the register GBA pokemon menu

6.It will ask to connect the GBA game

7.Open you GBA rom with VBA-M and when the credits screen appears (the black screen before the opening sequence) go to file and hit import save file

8.Now, yo should have a window explorer open asking to locate the save file for the VBA, while on the Dolphin is will say that connection failed

9.Press A on Pokemon Colloseum to go back and then hit again the register gba pokemon option

10.On the VBA, select your save file, import it and after a few seconds the two emulators will be connected