In Solar Opposites, Yumyulack shrinks various people (mostly adults) that make him angry, and puts them in a series of interconnected terrariums in the wall of his and Jesse's room. After the first episode, Yumyulack made an oath not to shrink down kids, and instead does it to various adults, putting them inside the wall.
At the end of the second episode, it was revealed that the wall was so much more. Over the time in which they have been stuck, the people in the wall have built a society, and some of the people in it were starting to become insane. A man named Tim and several other people were thrown inside the Wall, to which they were attacked by raiders and saved by a cloaked figure, who warns him to go ahead before more raiders arrive.
In the third episode, Yumyulack and Jesse dump candy and a woman into the Wall, in which it was revealed that there was so much more. The Wall had become a fully-fledged society with the sheer amount of people that were thrown in, with a military, a ruler, trade, and even religion.