The six that cost games, in the order they cost them.
Taking the Credit every turn on principle. Against the fastest quarter of the format the blocker is worth more than the resource, and this is the deck’s hardest habit to break.
Spending the round’s discount on the cheapest When Defeated unit instead of the most expensive one. The discount goes to the first one played, so the ordering is the whole decision.
Deploying into an empty board. The trigger needs another friendly unit, and without one you have spent your Epic Action on a 4/9 that will be answered.
Playing Pre Vizsla off printed HP. He reads remaining HP, and a damaged board is worth more to him than a fresh one.
Holding for something better after their leader has already deployed. The deployed leader is the something better.
Choosing the Lawbringer aspect before reading their leader and base. The choice happens on resolution and can be different every attack.