This expansion introduces Pokemon LV.X, which are leveled-up, more powerful Pokemon
Outside of these upgrades, we get an improved mana base, with channel lands and Mishra's Foundry, and a few sideboard improvements, like Reckoner Bankbuster for more card draw against control and Unlicensed Hearse over Lantern of the Lost for graveyard hate
Warning has those warriors deliver their warning through a really big horn
To me, it seems quite out of place in red/green, especially with the self-mill plan being green/black
With the format being in generally fast, lands are not really allowed to come in tapped, especially not when facing constant pressure of early threats like Ragavan or DRC
coupled with its lower damage output (160 damage) and heavier KO penalty (like all EX Mega Pokmon, Mega Latios EX being KO-ed instantly costs you the match), this makes it very undesirable to use seriously