Heres a general ratio you can follow Rough Breakdown of Cards by Cost We put this at about a 50/50 split as its important to have low cost cards for early game, and high cost cards for late game
Sorceress's Schemes is a red uncommon that pulls other instants or sorcery cards out of the graveyard or even exile, and - with the right helpers - creates an infinite loop that will ping your opponent to death
It often costs far less than 6 mana despite being an incredibly powerful threat, and its a devil to interact with between the immense ward cost that makes it hard to target and the triggered ability that makes it impossible to block
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While it only takes second place because its not quite as strong as the #1 spot, its got a lot going for it
This makes it one-sided, and the fact it minuses stats as opposed to doing damage means it gets around indestructible effects as well