The MTG Foundations release could result in some of these cards dropping in price, but its a bit too early to tell
If an effect instructs you to choose a card name, you may choose the alternative Adventure name
Their trigger reads, Whenever a land enters the battlefield under your control, you may gain control of target creature for as long as you control Roil Elemental. So, basically, as long as you can keep Roil Elemental alive, you can absolutely steal every other Creature on the battlefield
This card is a great card draw engine for white, most white decks could use it, and Turtles has its second ever version
For example, if you control Muldrotha, the Gravetide ("During each of your turns, you may play a land and cast a permanent spell of each permanent type from your graveyard") and you cast a creature spell from your graveyard during your second main phase, you won't be able to cast another creature spell from your graveyard with Muldrotha's permission until after your next ending phase ends