This secret achievement is very simple to complete all you need to do is unlock a Minidoll Figure.
Unlocking these figures are very random, if you have progressed enough in the game to visit a shop you need to either purchase or open Character Relics at 50,000 studs. As soon as you know you have one unlocked.
to open your character collectable men.
to scroll to Characters.
Now move your left analogue stick to your Minidoll then press
to select then back out with
Then pop achievement unlocked!
Here is a list of a few Minidolls encase unsure:General Mayhem
Wonder Women (Minidoll)