Again super mario maker 2 adds new elements to the players in the story mode in this opportunity has inserted the gray blocks that obstruct several things in super mario 3d world, these are new to the standard platform and you will have to go far enough in the game to to be able to break them, because to destroy them is essential to have higher coins.
To break gray blocks in super mario maker 2 the first thing must be to make mario transform into mario builder, that is the super hammer there is no other way to break the gray blocks that are practically at all levels.
On the other hand you must release the super hammer because it is really necessary for you to get to those specific areas of the game Super Mario maker 2 to other levels.
Well now that you know, you can take a look back at levels before, and you'll see that there you will get useful elements that would help you to climb more complex levels.
Remember that to break the gray blocks you must use the super hammer to pass, the most viable way would be to return in the game and reproduce through the 3d world history mode the previous levels, because somewhere along the way you will get gray blocks , you just have to transform yourself into mario builder, jump a little, press them and thus you can break gray blocks in that way you will keep the coins that is what you have been looking for in super mario maker 2.