Only double legendary creatures isnt that great, and youll still rack up two enters-the-battlefield or cool death triggers
He can deal a lot of damage in a red deck that focuses on burn spells in particular
The craziest card I know of is Warp World (5RRR, sorcery) which dumps all of your permanents into your graveyard and then you draw that many cards and put those permanents onto the battlefield
As for negotiating itself, go watch a few episodes of Pawn Stars
Its kind of a mediocre card, but it does let us use the Demonic Pact for something more productive than You lose the game. Anguished Unmaking is primarily a removal spell here, but its nice to have the option to go after our Pact when things get hairy
This guide will help give a quick explanation of what Commander is, and what to expect from each deck to help you pick the right oneassuming you dont grab all of them, that is