A Plunko Board is necessary to prestige. To prestige you need to build a Plunko Board and assign 76 cubbies to it. When you prestige, you have all the building dropped on the board. There are 5 slots at the bottom of the board, (1x, 3x, 5x, 3x and then 1x) based on where the building lands, you get a certain amount of Plunko points ( if the build lands on 5x its 5 times it normal value in Plunko points) the points then get traded in for briefcases.
after you prestige your town is reset, and your buildings are traded in for there value in Angel Wings and your angel buildings are refunded.