Gideon, Ally of Zendikar will be a Standard staple with potential for Modern as well. Not might be a Standard staple—will be.
Let’s ignore the “ultimate” (the third ability) and compare it to Xenagos. It doesn’t make mana and the tokens don’t have haste, but it requires only 1 color of mana, starts on 4 loyalty, attacks for 7 (!) the turn after you play it, and triggers Ally creatures you might have in play.
That “ultimate” that’s available right away is huge. It costs 1 more mana than Glorious Anthem to get into play when using it that way, but it can’t be removed (by cards that exist as I write this) and you don’t have to pop it right away. You might want to make a Knight or two, or attack once or twice, then go into Anthem mode. Or you might just tick up Gideon the turn you drop him, threatening to have an Anthem and a Gideon on the following turn.
Combine these modes and you have something that’s both powerful and flexible at a cost of 4 mana. You can combine this card with a White Weenie strategy, a tokens strategy, a planeswalkers (threat-light to blank their Doom Blades) strategy, and almost anything else you can think of capable of producing 2WW.
It’s not all upside. There is competition at Gideon and competition at 4 mana. Kytheon transforms into a Gideon which hurts this card a little in the White Weenie context. And 4-drops are usually pretty easy to find. I’ve staked some of my reputation here on this card emerging from that scrum as the 4-drop many people will choose to play, but even I am occasionally wrong.
A couple things to note: this Gideon ticks up while beating down. In the past we’ve seen some 0: abilities that turn Gideon into an indestructible creature. Players with those iterations had to decide whether to take a turn off from increasing Gideon’s loyalty in order to get him into the red zone. Now, with this Gideon, attacking not only threatens 5 damage, it threatens an Anthem the following turn (leaving Gideon around at 1 Loyalty). It’s just nice to progress while you’re turning sideways.
Next, I’ll note that as Constructed-playable Ally creatures get spoiled, Gideon’s stock will rise. This goes for Battle for Zendikar and potentially the next set in the block as well. You already want to play Gideon, if there’s also an Ally you feel like you want to be playing (something with a good rate and/or a unique impact on the board) these cards are going to form the backbone of a deck in my opinion. If you don’t spot it, Craig Wescoe will.
Gideon protects himself. The number of planeswalkers that cost 4 or less and are able to protect themselves from being attacked is not that long, and for good reason. At the turn 3-5 stage of the game, it’s difficult for most opponents to have multiple threats, large evasive threats, and to have them survive trades or removal you were able to muster up in your earlier turns. Sorin, Solemn Visitor and Sorin, Lord of Innistrad both saw plenty of play despite being multicolor cards, and both are pretty clearly inferior cards to Gideon, despite having a similar focus on token strategies. This is part of why I predict success for Gideon, Ally of Zendikar.