Special Zoom activates when a fighter is hit by certain attacks: the background flashes blue with dramatic "spark" effects pointing towards the action. If there are only two players on screen, time slows down substantially, and the camera zooms in on the point of impact. This slowdown effect only lasts for a short moment in 1v1s and even shorter in games with more than two players, and is usually accompanied by the sound effect previously only used by Little Mac's KO Uppercut in Super Smash Bros. 4. KO Uppercut, which previously had its own slowdown effect, now uses Special Zoom, as does Cloud's Limit Break special moves. During some Special Zoom events, camera control is disabled, though this is not consistently enforced.
In general, the most common attacks that trigger the Special Zoom effect are slow, hard-to-hit attacks (such as Warlock Punch or Falcon Punch). However, most other attacks that trigger Special Zoom have conditions that need to be met, such as Ridley's Skewer needing to be sweetspotted, or Little Mac's smash attacks requiring his armor to be triggered during the start-up. Certain items and stage hazards may also trigger this effect, similarly requiring special conditions in some cases.
Similar to Special Zoom is Finish Zoom or Final Zoom, terms also coined by Sakurai and his team. Finish Zoom is used when an attack will likely result in a game-winning KO. Like the Deadly Blow mechanic introduced in Super Smash Bros. 4, this effect does not factor in DI being used to make an otherwise-deadly blow survivable. Like Special Zoom, Finish Zoom zooms in on the point of impact and briefly slows down time. However, Finish Zoom uses a red background instead of a blue one, and the sound is always the same. The sound used is also different again, being akin to a ping hit combined with the sound of slashing swords.
List of moves that trigger Special Zoom
By assist trophy
By stage hazard