Of the black legendaries in the set, I really love Shadowheart, Dark Justiciar, who is an excellent Commander and card in the 99 of decks with big creatures
If youre playing spells that care about how many Gates you have, you should use lots of Gates
If youre about to lose a token at the end of your turn anyway, you might as well feed it into the altar for extra mana to fuel the next big move
If you get it, you should feel free to switch to an alternate Commander, as many of the decks have the best guy off in hiding
Im not saying those combos are bad, I just dont believe its correct to run Persistent Petitioners if you arent using them as your main wincon
Zuran Orb combined with Armageddon or opposed land destruction to flat out give you a giant life swing on cards already headed for the graveyard, and Balance and Land Tax are even better