#140 Favourite Brick Friday: 24201 2x1 Inverted Slope
This piece, although simple, became a life saver for many builders when it was released in 2015. As the smallest curved/rounded inverted slope that comes in a variety of colours, it is great at fitting into any MOC to provide a smooth surface.
Before 2015 there was no piece like it and the underside of MOCs tended to look blocky and unfinished. Now, the underside of builds can be shown and this piece is used to finish them off. It mimics the design of a 2x1 Slope when upside down, and therefore is great at transitioning for steps of bricks.
Here is the piece on Bricklink: https://www.bricklink.com/v2/catalog/catalogitem.page?id=143752#T=C