is the 100th episode of The Flash , originally airing on December 4, 2018. It serves as a commemorative milestone that balances a trip down memory lane with the urgent need to defeat the season’s "Big Bad," Cicada. Critical Consensus
: Includes guest stars Michelle Harrison, John Wesley Shipp, and Teddy Sears. [S5E8] What's Past is Prologue
: The episode succeeds in showing Nora the darker parts of her father’s history, though IGN argued it didn't fully realize its potential for deeper character development beyond the nostalgia. is the 100th episode of The Flash ,