Flinch

Flinching, also called Hitstun is what happens to a character when they are hit by an attack. The character will be stunned for a very short period of time, usually just enough to interrupt any attacks or movements. There are certain attacks that do not cause flinching, and ways for a character to avoid flinching. The amount of flinching is referred to as hitstun. Some attacks cause flinching without any knockback whatsoever. It is used for combos in all 3 smash games.

Attacks that do not cause flinching

• Fox's Blaster (except in SSB64)
• Mario's F.L.U.D.D. (no damage)
• Dr. Mario's and Mario's Cape
• Squirtle's charged Water Gun (no damage)
• Luigi's Super Jump Punch (only in Melee)
• Link's Gale Boomerang (on the return) (no damage)
• Ness's PSI Magnet (no damage)
• Snake's thrown Grenade (not the explosion)
• Olimar's Pikmin when latched on
• Mr. Game & Watch's Judge number 1
• The flame of Charizard's forward aerial
• The rain that occurs in the "Kitty Cover" game in the stage WarioWare, Inc.
• Glancing Blows (no damage)

Attacks that cause flinching with no knockback

• First hit of Ganondorf's Down Smash
• First hit of Lucario Down aerial
• First hit of Olimar's Neutral A
• First hit of Peach's Neutral A
• First two hits of Sonic's Neutral A
• First hit of Sonic's Up aerial
• First two hits of Snake's Neutral A
• First three hits of Snake's Neutral aerial
• First three hits of Snake's Down aerial
• First hit of Snake's Forward tilt
• First hit of or Young Link's or Toon Link's Forward Smash
• Luigi's Super Jump Punch (in Melee and Brawl, non-sweetspotted)

Ways to prevent/reduce flinching

• Metal Box
• Super Mushroom
• Certain Stickers (only in the Subspace Emissary)
• Any moves that offer knockback resistance.
• Air dodging (Brawl only)

In the original Super Smash Bros., hitstun was extremely high. This meant that this game had the most extreme and arguably best combos, allowing almost every character to have a 0-death combo.

In Melee, hitstun was lowered but wasn't lowered so much that it didn't allow for any combos, because it still allowed for several, such as the Ken combo. The Top, High and Middle tiers all operated mostly on combo ability.

In Brawl, hitstun was severely lowered, something that the game is often criticized for. The opponent suffers very little stun after being hit and air dodging decreases it even further, meaning that the game has hardly any combos. Some exceptions are Peach, Kirby and Meta Knight, who all have fast enough moves (or a select few, in Peach's case) to combo fairly well, up to over 70% in some cases.