When you have a companion in your deck, no matter if its best-of-one or best-of-three, itll occupy one of your sideboard slots the last one, to be more precise
They can run the range from mass destruction or bounce, taxing or life drain effects, boons for your stuff, and repeatable abilities on permanents all the way to individual instants and sorceries
Naturally, this can shift the course of the game, especially if you use cards similar to Alma or Bruno where you can, more or less see and manipulate what is at the top of your deck in the first place
This versatile tutor can summon up anything you need, from a Badgermole Cub for extra ramp, to a Reclamation Sage to handle a tricky permanent, to Craterhoof Behemoth when it's time to win the game
[3] [4] The color of the card determines the color of the mana generated