The Mothership is an event that can occur in Salmon Run and the main feature of this said event.
The Mothership event can happen all Tides, always bringing with it a black night. The Mothership is in the air, far from reach, containing a high, never ending supply of boxes containing more Salmonids. During the whole shift, handfuls of Chinooks, which are pretty much Chums with a propeller helmet, will continuously bring the boxes from the Mothership to various places of the battleground at an overwhelming rhythm. If a box is placed, the Chinook will flee and the box will start generating Salmonids at a steady rate until it disappears, happening if it is taken down or until it runs out of Salmonids, which can be seen as the inside of the box is red (normally blue). Some Salmonids will also emerge normally from the sea during this event. If the time before it would release another Salmonid is shorter than the connection lag between you and a teammate when you destroy the box, it will be released anyway, since the box was still intact on the other teammate's screen.
The boxes seem to possess around 50 hp and as they are destroyed, they produce a small radius explosion, destroying nearby boxes and damaging really close Salmonids. The only way to obtain Golden Eggs is by defeating the Chinooks, which will be defeated if they are close enough from their box when it explodes. Please keep in mind that Snatchers come as usual.
Aside from all this, the Mothership itself will pose a threat. Twice per Mothership event, the Mothership will head toward the egg basket with the firm intention to reclaim its eggs. Once it is over the basket, it will use the vacuum it has under it to try to take eggs from you, doing it at a rate of around one egg per three seconds. The only way to prevent it from taking more is by dealing enough damage to it, making it fall back. Stolen eggs are lost for good.
When the Mothership starts heading toward the egg basket, Mr. Grizz will tell you, and will also talk again once the Mothership is halfway there.
After repelling the Mothership for a second time, it is possible to see it crashing in the distance.
The Mothership heads toward the egg basket at around 75 and 25 seconds.
Using the Sting Ray is a common and clever idea; by aiming at the boxes at its top, it's possible to damage the Mothership before it reaches the basket AND both stop the arrival of boxes during that time while getting easy eggs.
Damaging the Mothership before it goes toward the basket is useless, as it will heal of all damage prior to doing so.