It’s a cosmetic-only event, where the cosmetics are either paid or can be earned by picking up easily-missed white objects that don’t show on the map and the pet will ignore.
One of the youtubers stated that a poorly executed event was worse than no event, and now that I am seeing this in practice I have to agree. This is a non-event. I wish Blizzard had put half as much thought into the gameplay as they did into the hype animation.