Brick Blocks are starting blocks in Super Mario Maker. Power-ups, enemies, Coins or Vines can be put in them, much like Question Blocks . They break after being hit by big Mario, or any power-up that makes Mario bigger, unless they have something in them, in which case they become Empty Blocks. The Brick Block is replaced by a different Block in the SMW skin, acting much differently than the regular Brick Block.
The Brick Block can be broken by the Thwomp or a thrown Shell, and turns into a Coin (if empty) under the effect of a P-Switch.