No. Hushbringer will not stop you from bringing Yorion, Sky Nomad into the game with its companion ability (note that companion was changed so a player pays at sorcery speed to put the companion into their hand from outside the game instead of casting it directly, but this doesn't affect the answer).
Hushbringer will, however, prevent Yorion's enters-the-battlefield ability from triggering when you do cast it.
February 28, 2021 6:20 a.m.
February 28, 2021 8:21 a.m.
Hushbringer doesn't interact with the companion ability at all. Companion lets you pull the companion from outside the game one time if you've satisfied the deck requirement and declared the creature as your companion beforehand. Hushbringer's effect has nothing to do with any of that.
What it does prevent is enters-the-battlefield abilities. Yorion also has one of those, so Hushbringer will stop that from working and you won't flicker anything when Yorion comes into play.