There are three achievements: get 5 medallions, get 25 medallions, and get all medallions.
My question is, what are medallions? Are they the little medal you get when you get every single lum in a level? (usually about 350) Or is a medallion the medal insert that your electoons go into, so a completed medallion involves the three cages, two lum collections, and one speed electoon?
If it's the former, this Platinum is going to be impossible to get... --- you'd play it for maybe a week or so then put it in the closet and never look at it again. just like my childhood. why didn't you love me dad? why? superblah750
I got the platinum a week or two ago, it isn't impossible at all. It is 350 for most levels, but that is not all the lums (although for some it may seem like it). The trick to some of them is to remember that each room is a checkpoint; if you mess up on a king lum's timing, or miss a giant bubble/coin, kill yourself and just start that room over. Also, remember you can touch the screen to pop lum bubbles and enemy bubbles.
No, the trophy is unlocked if you just get all the Electoons. I got mine fairly recently, and I got every Electoon in the game but did not get the little disco medal on the final stage when I got the trophy.