(This is the same basic principle why Giant Growth rocks by the way.) Each of these four creatures says if you jump through the right hoop, you can make your creature grow
While Ragavan, Nimble Pilferer has been looking more problematic and especially unfun in Vintage and Legacy (banned), its still relatively balanced in Modern
It works beautifully with cards that force sacrifice, especially in multiplayer: Butcher of Malakir, Plaguecrafter, or The Meathook Massacre
Rumbleweed, while not having Haste as much as you might look for it on there, is definitely a game-ender, especially if youve had Yuma spitting out those Plant Warriors for a few turns
Any "as [this permanent] enters" or "[this permanent] enters with" abilities of the copied permanent will also work