The brick block is an unused decoration block in Overstory. It has no purpose. 
Acid is a deadly liquid in Overstory that deals 1 damage when walked on. Using the bridge is recommended to cross these puddles. They are commonly mistaken for grass. 
The bridge is a block used to get around acid puddles 
In the first demo of Overstory, before the FPB, the battle scene was much more Undertale-themed. Boney’s bone would have been like Flowey’s “Friendliness pellets”, but re-textured to be a green bone. 