mtg all adventure cards Wilds of Eldraine best cards: what to look out for and Wizard.) You gain 3 life and draw three cards. Adventure - MTG Wiki

You are getting a ton of value for your seven mana, as you can exile your opponents best creature while putting a rather large threat in play

Yes, it's a colorless way to make infinite creatures if you have infinite mana, which is respectable but there's plenty of better ways to win with infinite mana

Mutavault will receive a +1/+1 counter only if it was a creature during the resolution of the last ability of Leyline of Abundance

Fortunately usually Temur players dont play more than one or two copies

Sacrificing it shields your entire board with hexproof and indestructible for the turn, making it a lifesaver against sweepers

The zero ability casually gives you three colorless mana - Combine this with the second part of the static ability, and any cheap, colorless spell (Expedition Map) is a removal spell