Here's a quick and easy way to round up all the rats at once in an entire room in Krusty's Super Fun House.

In any room where Krusty has at least two moveable blocks, position the first block near a wall. Wait until the rats have crossed and are between the wall and the block. While standing on top of the first block, release the block that Krusty is carrying and trap the rats.

If the area where all of the rats are trapped is only as wide as one block, all the rats in that space will be compressed into a single rat. This is especially helpful in areas where Krusty must build stairs for the rats to climb in order to reach the trap.

Hope that helps!!!