There will be maybe 3 mechanics that will need to be learnt properly - Murmur, Some rooms in Shalls, Steamvault.
A couple of Pulls that need to be learnt in Slabs, Botanica and Mechanar.
So basically the first couple of weeks with greens/blues there will be wipes. Once People learn, easy badges.
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You sure? There are far more People standing around in full raid epics in City Hubs in Classic with a similar population to how it was in Vanilla.