Pokemon Trainers, be on high alert
We Can Do It Riveting Rigger references Rosie the Riveter from the classic "We Can Do It" World War II poster
When you consider that rares and mythics are far more valuable than commons and uncommons are, which are pretty easy for everyone to access, in practice, this means that for every pack of The Brothers War you buy (assuming you eventually buy 10 to get the Golden Pack), you are essentially getting 1.6 packs worth of value, making Golden Packs perhaps the most generous improvement to the Arena economy ever
Since The Ur-Dragon has massive stats, you'll generally want to be attacking with it, however
Speaking of, I don't find its activated ability to be too great either
But if time is the limited resource that is spent flipping sieges, players will probably prefer a more meaningful threat to reward them for that effort and hopefully end the game sooner