Fun fact: Did you know Teferi, Time Raveler stops Emergent Ultimatum
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Each player who does draws seven cards
There is a way to template the ability so that it technically reads a little more blue (for example, instead of preventing the casting, it could allow it and then counter it) but it would just have been significantly wordier and would have had the same basic effect
So if you have 10 creatures on your board, you can pay just to put in your hand 7 of your cards and if they happen to be instants or sorceries, Witherbloom will discount them too, of course
Other sets may not have a heavy knight theme but still feature powerful individual knightslike Wight of the Reliquary in Modern Horizons 3