We made the ETB effect a combination of card draw and card filtering, thus increasing your chances of drawing the cards you need to win the battle, and maybe even the card you'll later copy with the Overloaded Mage-Ring
Commanders such as Kenrith, the Returned King and Kinnan, Bonder Prodigy can quickly spiral out of control, so having an answer for them that doesn't stop your own activated abilities is fantastic
Green decks arent always the most combat-oriented, but its not difficult to imagine a base of Lotus Cobra, Eternal Witness, fetchlands, and Wasteland as a starting point to make Spring-Leaf Avenger work
After the release on May 27, these cards may also be crafted using Wildcards
And its always just a land when needed
You could write entire best-of articles for constructs, equipment, mana rocks, myr, thopters, and so on (and we have!), so check those out for more comprehensive lists of those individual types of cards