Unfortunately, to play it you have to discard 2 cards which is a huge cost
Gix, Yawgmoth Praetor Gix, Yawgmoth Praetor is a nice 3-drop in black aggro decks to keep drawing cards after you hit opponents and add a nice Curiosity effect
your commander is gonna be 1-2 punching people, doubling your mana is gonna waste a turn, and you cant do alot with the mana other then empty your hand, and then you get boardwiped and your sent back to your childhood
Anyway his ability to protect an actually important planeswalker is decent
Seven mana for its bestow cost is very expensive, but any 5-color deck already runs mana-fixing and -ramping abilities to combat this
Additionally, you can just ignore the deck-building rule and include creature cards with companion in your main deck