Well,the card speaks for itself in terms of viability. It's amazing. Instead, here are all the Grass Pokemon in the format that would benefit from this.
-Mega Venusaur-EX (It already gained Mega Turbo, so now you can play it down during turn 1 to avoid having a first turn where you wait until the turn AFTER that turn to evolve.)
-Shiftry FLF (Good attacker, good draw support, and you're quicker now with the Stadium)
-Mega Heracross-EX (Same as Venusaur)
-Venomoth PHF (Never really saw play, but now that it can set up faster, it seems like it could be a good stall card)
-Yanmega PHF (Again, setting up quicker allows it to actually be useful with Windfall)
-Sceptile PRC (I see so many people on TCGONE using this with Trevenant-EX, so now it can actually work)
-Ludicolo PRC (I know it's still kind of inconsistent since it relies on a coin flip, but you never know.)
-Beautifly RSK (We need Safeguard that's reliable in XY-on, and now we somewhat have it. Much slower, though.)
-Vileplume ANC (It will probably see play anyway, so now it has a tool to make it even better. I know it's not good to predict playability before a card releases, but it's a reprint, so we know it'll at least be somewhat good. AZ COMBO EQUALS BROKEN)
Here's an extension of my original post theming off of the Expanded Format:
-Serperior BW (Good for healing, so think of it as a slower but stronger version of Jynx FUF.)
-Amoonguss NXD (No more waiting a turn to Poison, but probably won't do much outside of Ninetales decks because you can't use Virbank.)
-Venusaur DEX (Did this card ever see play? Not sure if it did, but searching out a Venusaur so you can search indefenitely for the rest of the game is amazing. I've been testing Expanded Garchomp recently, and Gabite helps swarm amazingly, so this could be fun, yet gimmicky.
-Accelgor DEX (Accelgor's already one of the best Expanded-exclusive decks right next to Huntail/Ho-Oh and Rayquaza/Eelektrik, but now you can start Decking and Covering turn 1. Who doesn't love being auto-paralyzed during the first turn?)
-Roserade DRX (It's a free search anywhere when you play it down, so it essentialy turns any copy of AZ or a ScoopUp-effect into a Computer Search. Nice.)
-Vileplume BCR (I've seen some really fun gimmick decks using this with Pachirisu, so now you can set up as needed. Could be a budget deck.)
-Cherrim PLS (It's a double Jynx. That sounds strong.)
-Exeggutor PLF (It may be losing steam with the rise in Shaymin-EX, but I still think that Exeggutor is slightly competitive.)
Man, the Pokemon Company is on a roll with all of this hype that it's generating. I haven't felt this excited for a set since Furious Fists (which turned out to be kind of messy), so I can't wait to see what else they've got in store!