either playing lands, drawing cards, or casting spells
Case in point, see the Amonkhet plains that was posted above
You can also use it to remove a creature and start attacking, and flash lets you do all of this while holding up other interactive pieces
The Emissary can find zombies but you have to pay extra mana to flip them and you lose the EtB effect of them as well which greatly reduces the value of a couple of the more top end ones
Ultros, Obnoxious Octopus Ultros has too many teeth (though thats accurate to the games), and is a great card for limited with letting your midrange spells ice opposing creatures, while the 8 mana thing left to the realm of casual play in large
It's here for that ETB to draw two and then discard two too, unless you discarded an artifact