Nickelodeon Kart Racers 2: Grand Prix

FYI - This only seems to count for the ones you actually collect on track so even if you total is greater than 500 some of those may be from win bonuses. To see how many you have collected, from main menu go to EXTRAS --> RECORDS --> MISC. and it's beside "Slime Tokens from tracks".

Just wanted to write that this is not cumulative. I did the “Add to Kart” achievement and this unlocked for me at 256 slime.