can any card be a commander mtg Which is Your D&D Class? Am I able to use

The Chaos Incarnate deck is themed around Rakdos (black/red) cards and uses Kardur, Doomscourge as a commander to wreak chaos all around the battlefield and force your opponents to attack each other

Smile at Death Smile at Death is an incredible value engine, and being able to get two creatures and even buff them spells doom for your opponents

You can have up to 15 different lesson cards in your sideboard in BO3, but that wont allow you to have any other regular sideboard cards

Cards like Thundermaw Hellkite are fantastic threats too, and great finishers, but they rarely do the whole job, they rely on other cards having done a lot of prior work