Naturally, you need the wall of text to truly appreciate the strength of this one
Mega Latias ex is just extraordinary, while the Mega Lucario ex seems to be deliberately evoking the classic Mewtwo vs Charizard cards of the Sword & Shield era, as the Lucario soars over a city, wheeling back to punch an attacking Venusaur
Thats where the Planechase Set shines
Especially since the printings of Ragavan, Nimble Pilferer and Dragons Rage Channeler, the steal a casting cost 1 nonland-permanent mode has become very important and overall buffed the playability of the card
Now it is also a fine tool against aggro and midrange decks so much that you are pretty happy running it main in most cases
Remember how Kiki-Jiki, Mirror Breaker can make infinite creatures