FX Volume
A box in the level that plays effects for the player who walks into it: an impact as they come in, an overlay while they're inside, or a transition. The same one every time, each in turn, or one at random.
Drag a Blendable FX Volume into the level from Place Actors, size its box, and give it effects. It's drawn in the viewport in the effects' own orange, with the plugin's mark at its centre so you can find it in a busy level. Neither shows in the game.
Plays.
An Impact As You Come In; An Overlay While You're Inside, gone as you leave; or A Transition As You Come In, which covers and reveals with nothing changed underneath, for trying transitions out.
Effects.
The effects it plays.
And Every Effect In.
Folders whose effects it plays too, after Effects, the folders inside them included. They're gathered again as play begins in the editor, so an effect added to a folder since plays without touching the level.
Picks.
The First every time, Each In Turn round and round, or one At Random, never the same twice running.
Plays At.
Where an effect centred Where It's Played strikes: on Whoever Came In, on The Volume, or on An Actor you choose, followed as it moves.
Show Its Name.
Prints each effect's name on screen as it plays, with where it is in the list. Development builds only.
Play For plays its next effect for a player as walking in does, from Blueprint. Enabled turns it off without removing it; walking out still takes away an overlay it showed.
Go deeperHow a packaged game gets a folder's effects
Folders are gathered in the editor and saved with the volume as soft references, which the cook follows, so a packaged game has every effect the volume names even though nothing else refers to them. In the editor they're gathered again as play begins, so the list is always what the folders hold now.