You also drop an extra land this turn, so if you exiled two lands, you can drop both this turn, and if three, two this turn and one next
And while her ability is certainly pretty cool, I doubt it will be strong enough to tempt players to include it in their decks
Your opponent will defend, you'll hopefully win (with a Lightning Strike tipping the scales), and then A-Raiyuu will trigger a second attack to crush your opponent's defenses
Sure, it's only once a turn, but it's also capable of triggering on your opponents turns, making it wildly good in Commander, where you have three other people playing
Olivia, Opulent Outlaw Any treasure commander deserves a little respect, but Olivia, Opulent Outlaw commands much more
Nascent Metamorph becomes a copy of that creature until end of turn