How to get a Dream Ball?

Question

I sometimes heard things about a dream ball.
and I saw once on youtube that somone had caught a regigigas with one. it also said: 'a fatal appearance' or something.

Answer 1

In Sword and Shield, for the first time since Generation 5, Dream Balls are available once more, yet they are finite.

When you speak to Ball Guy in Wyndon for the first time, he will give you a Dream Ball.

Between May 21 to May 28, 2020, a Mystery Gift was available that gave you a Dream Ball, among other things.

Source

Answer 2

It is a ball in Pokemon Black/White that can only be used in Highlink Forest. It suddenly appears in your bag. Look at This:

http://serebii.net/itemdex/dreamballshtml