It is indeed only the Reverse Roly Poly that you are missing. I think the thing to do would be to find one and use a cheat like Ultra Hammer Up to get the firepower to defeat it. I don’t really have any tips on the minigames… I recall the net game involving some amount of luck. I think I ended up grinding coins using Who Doesn’t Want To Be a Moron.
Viewing post in Gallery Goal - "Beating One of Everything"
I'm also trying to get through without cheats, so there's that >_< and creating my own world in order to scan missing monsters worked for the "scan" goal, but for some reason self-created worlds don't count towards the coin or "defeat monsters" goal... oh well X3 keep looking for a level with one that includes powerups I guess, thanks for the confirmation ^^
and yeah, years ago I also used Moron for coin, I might end up doing that again but there's some good levels that give you crazy coin as well.