Golden Strawberries
Golden Strawberries are special berries, tinted gold in color and with a crown on top, which are first unlocked upon completing Chapter 8B. They are only collected at the last screens of the chapter in A-sides and upon collecting a heart in B-sides and C-sides. They appear at the start of every chapter, with the exception of 6A, 8 (all sides) and 9.
Each level here on the Celeste Wiki will have a guide with strategies on collecting Golden Strawberries. However, doing as such usually does not suffice; speedrun tech, such as hyperdashes and wavedashes, are often strongly recommended. Generally speaking, most people collect C-Side Golden Strawberries first, owing to their short length, before collecting A-Side ones. B-Sides are generally the hardest, because they share both length and difficulty.
Unlike practicing for speedruns, obtaining a Golden Strawberry is all about consistency, and being able to make it across a large number of rooms without dying once.