Both commanders start in the command zone, and the remaining 98 cards (or 58 cards in a Commander Draft game) of your deck are shuffled to become your library
The issue is that there is not enough of the generally playable one mana options for one person, let alone two people in the colour, not that there are not enough total to have black fully covered for its potential needs in the discard department
If you already know what order the sets launched in, working this out is easy: The First Chapter has a "1", Rise Of The Floodborn has "2" , and so on
This is a good card to play when theres a particular opposing character you really want to get rid of this turn, especially if you have something that can take the hits like a champ think Goofy, Knight for a Day or Lumiere, Hotheaded Candelabra
All you need to do is banish this card and a prince