Plot elements are things like doors that need to be opened somehow, or platforms that appear so you can cross otherwise impassable areas. They are typically used in single-player games like Doom. Note that in Syntensity they function in multiplayer mode as well (there is no 'singleplayer mode' or 'multiplayer mode' in Syntensity - all games are always multiplayer-ready. But you can also play them locally with just one player, if you want).
As the video shows, when in edit mode you can see some visualization hints, like effects connecting doors and platforms to the triggers that activate them. The visualization hints show both what is connected to what and in what direction.
There are some other features of plot elements not shown in the video:
- You can have multiple triggers for a door or a platform, so the player(s) need to trigger them all before it opens.
- A trigger can also be defined to hold an item. In that case, to open the thing it is connected to, the player must reach the trigger, at which point they get the item, and then they must bring it to the right place.