mtg modern horizons 3 most expensive cards mh3 The 38 Most Expensive and

Central with a 15-minute extended bidding window on certain items

While none of the individual cards are truly broken on their own, the mechanic itself arguably broke the Commander format, at least on a competitive level

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Put two +1/+1 counters on each creature you control

From there, it really depends upon the deck and what I'm trying to do, but those three categories are essential