There are some more minor options in Red and Black utilizing more of a ritual-style ramp effect, but outright ramps is a bit more of a rarity, especially on ETB creatures
For 2W, shes cheap to play, buffed by legendary permanents, and incidentally allows us to seek out legendary cards from the deck based on her strength
This can go both ways as you can either opt to mill your opponents or self-mill to create massive card advantage
Primarily both are played as a two drop that draws a card, the elf is just a body to be done away with via Skullclamps etc or offer up synergy for better elves where as the wall is more of a speedbump against aggressive decks
It can be used to flicker any of your team's creatures if they have a good enter the battlefield ability
The Eldrazi are otherworldly beings of great hunger and power that all-but annihilated the planes of Zendikar and Innistrad, and that power can be yours (in Commander)