And, because its another early, rare MTG card, its valued in the thousands
Death's Oasis is pretty straightforward: whenever one of our non-token creatures dies, we get to mill two cards and then return a creature of lesser converted mana cost to our hand
If you don't, it gains haste." If Rhythm of the Wild leaves the battlefield at the same time that a nontoken creature enters (most likely because that creature has a replacement effect that modifies how it enters, such as Rescuer Sphinx from the War of the Spark release), that creature still gets a +1/+1 counter or haste
One your mana was doubled there were any number of ways to start generating massive card advantage and take over the game in short order, with Wrath of God serving as the four-drop to lead into the Wake and Mirari itself, which was usually the way things ended
Many full art MTG cards have elements that flow over the frame elements, but I think Ikoria did it best, and that tentacle here is just awesome