Agro is a very loyal horse to Wander, and it quickly becomes clear during the game that the two have been together for a long time. After each colossus falls, Wander awakens in the central Shrine, where Agro is seen galloping in a few seconds later. Agro's speed helps Wander in many battles, by either keeping him from harm (versus Basaran and Dirge) or allowing him to catch up with a fast-moving enemy (Phalanx).
Before the final colossus, Wander must cross a collapsing bridge that he cannot cross fast enough on his own. He runs across with Agro, but even she falls short just before the end. Agro bucks Wander to safety and falls into the chasm below, while Wander watches helplessly.
After Dormin and Wander have been consumed by the whirlwind in the Shrine and Mono reawakens, Agro is revealed to be alive, but has suffered an injured hind leg and limps. It is not clear if Mono recognizes the horse, but she follows her to the stone basin at the back of the Shrine - revealing the horned infant Wander - and onwards to the mysterious garden above.
Gender ConfusionThere has been a lot of confusion and debate about Agro's gender. Fortunately, Fumito Ueda has confirmed Agro's gender as 'a girl' in an interview in the official artbook and guidebook. Many fans still believe Agro is a stallion, due to the mistranslation (where Agro is referred to as male) in a tutorial message.
Agro has a diamond-shaped patch of white fur on her head between her eyes. If there is a save file from Ico on the same memory card when a new game is created, Agro will have an "I"-shaped patch on her head from the Ico logo instead. Unfortunately, there is no way to "upgrade" the marking on Agro to an Ico symbol after a game has been started and saved; the only way to get the "I" marking is to start a brand new game with an Ico save file. There is one exception to this: starting a session of Time Attack with an Ico save file on the same Memory Card will change Agro's symbol to the "Ico I" (provided you chose one of the five colossi Agro can make it to), but the symbol will return to the regular design once you go back to the Shrine.
Two different colors for Agro can also be unlocked: brown and white. To unlock Brown Agro, you must clear all 16 challenges in Time Attack. For White Agro, you must clear every challenge in Time Attack on both Normal and Hard. You will be notified when you have successfully unlocked both Agro colors, as well as how to access them: to change to Brown Agro (or from brown back to default), hold down at the title screen while selecting Load Game. To change to White Agro (or from white back to default), hold down at the title screen while selecting Load Game.
- Given that she can run at full speed for large distances, Agro is most likely a thoroughbred horse; built for endurance rather than bursts of short speed. The only confounding factor of this theory is that when measured against the colossi and Wander, she is as tall as real-life draft (heavy) horses.
- Agro's top speed is somewhere between 40 and 50 mph.
- If Wander points his bow and arrow at Agro, Agro will rear up and neigh before galloping away and out of the line of fire. Amusingly, she won't react when hit with the sword, and makes a metallic noise when struck.
- Agro will stop if she comes to a drop that is too big to jump, will turn and steer around objects by herself whilst Wander rides her and will slow down if she is traveling across, for example, a narrow path (such as the natural bridge that leads to Kuromori's lair).
- Agro can be injured by any of the colossi that she has access to (Quadratus, Phaedra, Basaran, Dirge and Phalanx). When she is injured, she will hobble briefly before returning to normal with no apparent permanent or long-lasting damage.
- In Greek Mythology, the Argo was the ship on which Jason and the Argonauts sailed from Lolcos to retrieve the Golden Fleece. Perhaps it is a reference to Agro being Wander's vessel in his quest.
- There is a glitch with Agro. If you defeat all 16 colossi in Normal Time Attack, collect all the items, and then die before saving your game, you won't have any items you had after the last time you saved. You will also have to defeat the colossi again to get the items back. If you do that, you will be able to have brown and white Agro in Normal mode.
- Although, many fans believe that Agro suffered a broken leg at the end of the game, it is much more plausible to say that it was only severely sprained, because if the actual bone was broken, the resulting pain would have certainly prevented her from swimming to shore, and limping all the way back to the shrine.