Rule of holding

You mean like the supporters in "Is it wrong to pickup a girl form a dungeon".

That has enough "Shulker Box inside Shulker Box" energy to make the universe implode.

Perhaps a bag of holding with many kobolds with many pockets? Which contain more bags with more kobolds with more pockets—

Truly the best of both worlds.

Labelled as “Oops! All Tucker’s kobolds!”