For reference, before the tax was added to the Companion mechanic, as long as you upheld the deckbuilding restriction that the Companion requested, you could add your Companion from the Companion zone (your sideboard) to your hand at no cost essentially allowing you to begin the game with a guaranteed extra card in hand
Plus particularly if you have green as a base color much of this fixing can get you any color of mana
They often target high-demand, high-dollar staples: Power 9, dual lands, Reserve List cards, and format-defining pieces
If youre about to move on to the next paragraph, I am going to highlight a bunch of specs based on the MOM preconstructed decks and you can skip right to it if you want
Since its colorless, it can go into a wide variety of decks and likely will
Ramp Mardu doesn't have a lot of traditional mana ramp options, but there are several mana rocks that also provide opportunities to roll the dice, a perfect fit for Mr