Riot tried to remove the double Zhonya's interaction by making Stopwatch no longer purchasable if you already own Guardian Angel or Zhonya's Hourglass.
But you are still able to use both, if you buy a second Stopwatch before upgrading your first one to Zhonya's or Guardian Angel.
surely this can’t be an oversight by riot right
Not an oversight, this was a conscious decision. That being said, we will be removing this in 12.9. We didn't have as much time to iron out the details of this change as we would have liked, so we made some calls what was immediately ok, and what we would reconsider for future patches.
Will 12.9 be out by MSI or will pro player in MSI be informed that they are not allowed to do this if game happens on 12.8?
12.8 is the MSI patch, these will be fixed for 12.9. We are currently deciding what to do about pro play.
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