The rarer, more popular, and more useful the card, the more expensive it is
(Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.) Instant Shriekmaw Fear (This creature can't be blocked except by artifact creatures and/or black creatures.) When this creature enters, destroy target nonartifact, nonblack creature
I expect that, most of the time, The Thirteenth Doctor will pick a Doctors companion with red in the color identity to unlock the various red draw into exile cards like Reckless Impulse
Some cards, like Gale - Wind Spirit, let players return the card to their hand when it is banished, while other cards allow players to draw new cards into their hand
The combination of ramp and card advantage makes this a nasty Sultai commander, and you even get a life buffer with the triggered ability