Just to add to what Cruezilla said,
To do this, you need a minimum of 5 people if you're prepared to 'play' each other more than once. This will allow you to boost wins to each round, rinse and repeat. Earlier on this afternoon, we had 8 in a party and we were zipping through various rounds left right and center - it seemed it took forever for 1 person to get the win and the about an hour for the other 7.
Finding each other seemed to go in waves. For 15-20 minutes, we'd find each other in a search very quickly. After a while (usually when Cruezilla pointed out how well it was going...) we'd find ourselves not picking up matches - bear with it, it'll come good eventually.
Country of origin doesn't affect searches either. We had users from England, Scotland, Germany, USA and Canada and could find each other (granted some a little easier than others but still, it is possible).
If you find yourself paired with someone that isn't in your party, you have 5 minutes to quit the game before it counts as a loss in that round. Obviously, you need the ball to be able to pause and quit so if you find yourself without possession at 4 minutes, dashboard! The 5 minute rule also applies to you quitting out for the boost as well. Our method was an own goal and quitting out at 5:01 and after - this worked every time.
Quitting also works in the final as well. Remember to always press B once you've won the cup and returned to the brackets screen. Pressing A will re-enter you into the cup and you won't get the achievement.
Finally, cheers to our party this afternoon. Plenty of laughs, we all got the achievements and even leveled up a bit in the process!
Amstrad CPC 464, Game Boy, SNES, Dreamcast, GBA XBOX, PSP, XBOX 360
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