This applies to any type of booster box, including set, draft, or Collector Boosters)
Palace Jailer Palace Jailer is the best creature to claim the monarchy with because removing a creature when it enters makes it much easier to maintain the crown
Features "Undying": returns to the battlefield with a +1/+1 counter if it dies without such counters
Elesh Norn, Mother of Machines This five-drop 4/7 legendary dork has vigilance, which is better in multiplayer since you can swing at the open player without opening yourself up to multiple counter attacks from everyone
Abby, Merciless Soldier Partner is generally a good ability to have and the one I think Abby, Merciless Soldier works best with is Joel, Resolute Survivor which makes great use of the tokens you get from casting Abby
Lazav, the Multifarious For just a blue and black mana, Lazav, the Multifarious, is a great card that capitalizes on having creatures in your graveyard