Oops Undo

'''Oops! - Undo''' is a mod that allows players to undo an action of block placement.

Meaning instead of placing Obsidian and you don't have a Diamond Pickaxe or just misplaced a block while building you can undo your placement.

Pretty sure that space in the player's inventory is necessary for it to work.

Video Review

Have you ever been building a giant wall out of obsidian and made an accidental placement only to have to cry in a corner in shame because you're inadequate? I know I have, 'Oops' was made to solve this problem, when 'Oops' is present you have 3 seconds to break the block you placed and get it right back, no need for a tool or anything! Take a look at these gifs to get an idea.