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
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
Sets have never had any variations in their booster box designs, other than the 1st edition stamps on older boxes, and Asian boxes which do differ
And, because its another early, rare MTG card, its valued in the thousands
Some people see this as a bad fetchland, but I see it as a license to play five-color decks in Modern