What's Past Is Prologue

Synopsis
In the 100th episode, Barry and Team Flash come up with a plan to stop Cicada. However, the plan calls for Barry and Nora to travel back in time to gather some key necessities. However, Barry hesitates, concerned about his daughter seeing certain parts of his life. Meanwhile, Sherloque takes his concerns about Nora to Iris, and Caitlin turns up a key asset in the fight against Cicada.

Protagonists

 * Team Flash
 * Harrison Sherloque Wells
 * Elongated Man (Ralph Dibny)
 * The Flash (Barry Allen)
 * Iris West-Allen
 * Vibe (Cisco Ramon)
 * Killer Frost (Caitlin Snow)
 * XS (Nora West-Allen)
 * The Flash (Barry Allen) (Earth-90)

Villains

 * Cicada (Orlin Dwyer)
 * Savitar
 * Clifford DeVoe
 * Zoom
 * Eobard Thawne
 * Time Wraith
 * Harrison Wells (Eobard Thawne)
 * The Monitor (Mar Novu)

Other Characters

 * Grace Gibbons
 * Grace Gibbons' Mother
 * Grace Gibbons' Father
 * Ronnie Raymond
 * Joe West
 * Henry Allen
 * Nora Allen
 * Gideon

Before March 18, 2000

 * Henry Allen
 * Nora Allen
 * God

December 11, 2013

 * S.T.A.R. Labs
 * Harrison Wells (Eobard Thawne)
 * Grodd
 * Cisco Ramon
 * Caitlin Snow
 * Ronnie Raymond
 * Hartley Rathaway
 * Clifford DeVoe
 * Marlize DeVoe
 * Barry Allen
 * Iris West
 * Gideon
 * Martin Stein
 * The Thinker (Clifford DeVoe)
 * Clyde Mardon
 * Mark Mardon
 * Vanessa Ambres

January 27, 2015

 * Barry Allen (2016)
 * Harrison Wells (Eobard Thawne)
 * Jesse Chambers
 * Libby Lawrence
 * Danica Williams
 * Dawn West-Allen
 * Dawn's Sibling
 * Savitar

April 29, 2016

 * Zoom/Jay Garrick (Hunter Zolomon)
 * Team Flash
 * Wally West
 * Iris West
 * Joe West
 * Caitlin Snow
 * Cisco Ramon
 * Harry Wells
 * Jesse Wells

May 23, 2017

 * Savitar (Barry Allen)
 * Team Flash
 * The Flash (Barry Allen)
 * Kid Flash (Wally West)
 * The Flash (Jay Garrick)
 * Killer Frost (Caitlin Snow)
 * Vibe (Cisco Ramon)
 * Iris West

Speed Force Visions

 * Team Flash
 * The Flash (Barry Allen)
 * The Flash (Iris West-Allen)
 * Gypsy (Cynthia)
 * The Flash (Jay Garrick)
 * Vibe (Cisco Ramon)
 * Killer Frost (Caitlin Snow)
 * Henry Allen
 * Edwin Gauss
 * The Thinker (Clifford DeVoe)
 * Marlize DeVoe
 * Nora Allen (Speed Force)
 * Grodd
 * Dominators
 * Hunter Zolomon
 * King Shark (Shay Lamden)
 * Reverse-Flash (Eobard Thawne)
 * Pied Piper (Hartley Rathaway)

Teams and Organizations

 * Central City Hospital
 * Team Flash
 * S.T.A.R. Labs
 * Szrek Chemicals
 * Flash Museum
 * Julian Medical Supplies

December 1, 2013

 * S.T.A.R. Labs
 * Rebooted Legion
 * CCPD
 * Central City Hospital

January 27, 2015

 * S.T.A.R. Labs

April 29, 2016

 * S.T.A.R. Labs

Species

 * Humans
 * Metahumans
 * Artificial Intelligence
 * Time Wraiths

December 11, 2013

 * Humans (Earth-221)
 * Humans
 * Metahumans
 * Gorillas
 * Artificial Intelligence

January 27, 2015

 * Humans
 * Metahumans

April 29, 2016

 * Humans
 * Humans (Earth-2)

May 23, 2017

 * Humans
 * Metahumans
 * Metahumans (Earth-3)
 * Time Remnants

Speed Force Visions

 * Humans
 * Metahumans
 * Metahumans
 * Metahumans
 * Metahumans
 * Time Remnants

Elseworlds Cold Open

 * Humans
 * Metahumans
 * Maltusians

Objects

 * Sally the Satellite
 * Lightning Dagger
 * Dark Matter
 * Dagger Dampener
 * Nora West-Allen's Journal
 * Time Language
 * Time Portal
 * Savitar's Suit
 * Speed Force Transmitter
 * Flash Ring
 * The Flash Suit
 * Power Dampener
 * Breaches
 * CFL Quark Matter
 * S.T.A.R. Labs Mobile Research Unit
 * Cicada Suit
 * Vibe Suit
 * Reverb Goggles
 * Vibe Gauntlets
 * XS Suit
 * Gauntlets
 * Elongated Man Suit
 * Enlightenment Satellites
 * Pulse Rifle
 * Tachyons

December 11, 2013

 * Reverse-Flash Suit
 * Dark Matter
 * Firestorm Matrix
 * Firestorm Matrix Core

January 27, 2015

 * The Flash Suit (2015)
 * Wheelchair
 * Dark Matter
 * Savitar's Suit

April 29, 2016

 * Zoom Suit
 * Pulse Rifle
 * Speed Force Transmitter
 * The Flash Suit
 * Breaches

May 23, 2017

 * Savitar's Suit
 * The Flash Suit
 * The Flash Suit (Earth-3)
 * Jay Garrick's Helmet
 * Speed Force Bazooka
 * Vibe Suit
 * Reverb Goggles
 * Vibe Gauntlets
 * Killer Frost Suit
 * Breaches

Speed Force Visions

 * The Flash Suits
 * Hoverchair
 * Elongated Man Suit
 * XS Suit
 * Gauntlets
 * Thinking Cap
 * Time Language
 * Breaches
 * Vibe Suits
 * Reverb Goggles
 * Vibe Gauntlets
 * Jay Garrick's Helmet
 * The Flash Suit
 * Savitar's Suit
 * Killer Frost Suit
 * Dominator Drop Ship
 * Zoom Suit
 * Reverse-Flash Suit
 * Pied Piper Suit

Elseworlds Cold Open

 * "Stargirl Suit"
 * "Hawkgirl Suit"
 * "Huntress Suit"
 * "Hawkman Suit"
 * "Green Arrow Suit (Earth-90)"
 * "Captain Cold Suit"
 * "Firestorm Suit"
 * "The Ray Suit"
 * "Jesse Quick Suit"
 * "Obsidian Suit"
 * The Flash Suit (Earth-90)

Locations

 * Earth-1
 * Earth
 * USA
 * Missouri
 * Central City
 * S.T.A.R. Labs Central City Facility
 * Pipeline
 * Time Vault
 * Flash Museum
 * Keystone City
 * Iron Heights Penitentiary
 * Earth-90
 * Earth
 * Speed Force

Prior to March 18, 2000

 * Earth-1
 * Earth
 * USA
 * Missouri
 * Central City
 * Holly Drive
 * Allen House

December 11, 2013

 * Earth-1
 * Earth
 * USA
 * Missouri
 * Central City
 * S.T.A.R. Labs Central City Facility
 * S.T.A.R. Labs Particle Accelerator
 * Time Vault
 * Central City Police Precinct

January 27, 2015

 * Earth-1
 * Earth
 * USA
 * Missouri
 * Central City
 * S.T.A.R. Labs Central City Facility
 * S.T.A.R. Labs Particle Accelerator
 * Time Vault

April 29, 2016

 * Earth-1
 * Earth
 * USA
 * Missouri
 * Central City
 * S.T.A.R. Labs Central City Facility
 * Earth-2

May 23, 2017

 * Earth-1
 * Earth
 * USA
 * Missouri
 * Central City

Speed Force Visions

 * Earth-1
 * Earth
 * USA
 * Missouri
 * Central City
 * S.T.A.R. Labs Central City Facility
 * Central City Police Precinct
 * Keystone City
 * Iron Heights Penitentiary
 * Earth-2
 * Gorilla City
 * The Thinker's Sanctuary