You need to PAY again (regardless of whether you have a premium pass) to get all the rewards. Something that was supposed to be a gift at the end of the year, Blizzard managed to find a way to massively monetize it.
How so? Literally play games each week and you get 120 tickets. Enough to buy the skins that cost 90 each. If you get the premium then you can get multiple skins. Where in ow2 events at best we get 1 free skin, and then others are 20 dollar shop skins. Here you can get 3 more skins for 5 bucks instead. Its better than past ow2 events, which isnt saying much, but still.