
Gladehart Cavalry is the cover card of this intro pack. They cost a whopping 5GG - a total of seven mana. But when the Cavalry arrive, they offer quite a bit of Support. With Support 6, the Cavalry distributes a +1/+1 counter on each of up to six other target creatures. While this is pretty useful, it's important to recognize that you actually need the six other creatures to take full advantage of this ability.
The other cool thing about the Cavalry is that you get a second benefit, as well. Whenever you have a creature with a +1/+1 counter on it die, you gain 2 life. While this is purely incidental lifegain, you never know when you'll need those extra 2 points of life to keep you in the game.
Onto the rest of the deck!
Creature (26)
2 Cliffside Lookout
2 Expedition Envoy
2 Kitesail Scout
1 Oran-Rief Invoker
2 Kor Castigator
2 Makindi Aeronaut
2 Kor Sky Climber
2 Shadow Glider
2 Joraga Auxiliary
1 Veteran Warleader
1 Saddleback Lagac
2 Relief Captain
1 Steppe Glider
2 Expedition Raptor
1 Angel of Renewal
1 Gladehart Cavalry
Sorcery (10)
2 Shoulder to Shoulder
1 Allied Reinforcements
2 Lead by Example
1 Immolating Glare
1 Mighty Leap
1 Iona's Blessing
2 Isolation Zone
Land (24)
1 Evolving Wilds
1 Tranquil Expanse
7 Forest
15 Plains

Whereas the Red/White "Desperate Stand" deck focuses on the Cohort mechanic, this deck focuses on the Support mechanic introduced by Gladehart Cavalry.
In addition to the support creatures, there's two copies of Shoulder to Shoulder, a 2W sorcery with Support 2 that also draws you a card. The instant Lead by Example is 1G and also has Support 2 but doesn't draw you a card. Having Instant speed is really good to have as it can be a combat trick.
Support is on the slower side as a Mechanic and really requires you to consistently have two or three other creatures on the board to take full advantage of regularly. But whereas Cohort requires you to consistently tap two creatures for a generally underwhelming effect, Support adds power and toughness fairly quickly, even if it doing so often takes up entire turns at times.

Support is an interesting mechanic, and in a Limited environment (draft and sealed deck) could be pretty good to build around. But from a Constructed standpoint, it's a bit underwhelming. The best direction to go with this Green/White Allies archetype is to run something similar to this Green/White Allies deck that actually placed second at a Wyoming States tournament. It's fueled by Collected Company to accelerate getting more Allies into play. That list, which includes Kor Bladewhirl and Lantern Scout, is probably the direction you would want to go when upgrading the creature line-up.
Green/White Allies is definitely a playable deck, but the creatures with Support are generally not good enough to be played competitively. Also, while Gladehart Cavalry is a solid card in a vacuum - and is pretty good for Elf decks in Commander - it's a bit too high on the curve and offers too inconsistent a benefit to be a "boss" monster. Ally decks should focus on creatures lower on the mana curve. If you want to splash Red, you can even include Reckless Bushwhacker, who gives all your creatures haste and +1/+0 if you've cast at least one other spell already that turn. There's also Firemantle Mage who has the Rally trigger to give all of your creatures Haste whenever another Ally enters the battlefield.
If you want to play Allies, this isn't necessarily the strongest deck to start with. In comparison with the other Intro Pack, it probably holds up fine. But besides Expedition Envoy, Kor Castigator, and Veteran Warleader, there isn't much to build off of out of the box if you're looking to beef this deck up.