One makes a wish that the magic mirror could make lots of friends at once, and pretty soon it's pandemonium.
In Numberblock Castle, Numberblocks 1-10 walk to a long gallery. One peeks through a downward stairwell. She walks down and finds a mirror. It makes two Ones, who both add up to Two. Two decides they should make Three next. One tells the mirror her wish to make three Ones. The mirror becomes three and three Ones appear.
Next, Two tells the mirror to make two lots. Two Twos appear.
2 + 2 = 4
One wants to tell the others about it, and warns Two, Three, and Four to keep an eye on the mirror and not mess around with it. Three does it anyway and asks the mirror for two lots.
Next, Three asks the mirror for three lots.
3+3+3 = 9
Nine separates into the Three Threes. Three checks to make sure everyone's here, but Five is missing. Three wonders how many lots of which number is 5. Three puts Two at the magic mirror and asks for three lots.
3+3 = 6
Another Six appears, but Three says she's hoping for Five. Four tries the mirror and asks for two lots.
4+4 = 8
Three says they're also missing Seven and Ten and asks who wants to try next. Back upstairs, One leads the group to the basement. Back downstairs, five Twos appear.
2+2+2+2+2 = 10
All they need now is Five and Seven, but Two hears footsteps. He barricades the door and tries to get the others to hide. Two sees a closet door.
The basement door opens. The group sees nothing but a magic mirror, until an avalanche of Numberblocks tumble out of the closet, much to their... surprise!