Here is an overview of Flasback levels, via Activision:
“Flashback” levels will give players the ability to rewind time back to the 90s—the greatest era ever!
The Flashback levels are designed to challenge players’ puzzle solving and technical performing abilities. They also give fans even more ways to play. Through the collection of Flashback Tapes, players discover Crash and Coco’s origin story and experience Bandicoot training in Neo Cortex’s Test Chambers—but the task won’t be easy.
View a set of screenshots at the gallery.