My pick for the best card in Oath of the Gatewatch for Standard was Chandra, Flamecaller.
This planeswalker isn’t even trying to be innocuous. It’s clearly extremely powerful and needs a great shell to shine.
Temur may be the right answer.
Rattleclaw Mystic is a pretty perfect complement to Chandra, accelerating the planeswalker out on turn 4 when it can really take over a board.
Sylvan Advocate is another big Oath addition, providing an efficient body both early and late.
Advocate is at its best in a deck that can play a land as powerful as Lumbering Falls, so a Simic build makes a lot of sense.
The powerful mythic planeswalker could definitely be the perfect piece of the puzzle to making Temur a player in Standard going forward!