While Redcrosse is mysterious, Guyon, hero of Book 2, is just downright tricky. Not even critics of The Faerie Queene have been able to agree on this guy's sitch, so don't despair if you found yourself a wee bit puzzled. The confusion surrounding Guyon tends to center on two problems 1) Guyon's association with the virtue of Temperance, not the most obvious virtue out there and 2) whether or not Guyon actually embodies Temperance, whatever that means, and whether Temperance can really make someone a hero.
Strictly defined, Temperance is the virtue of self-restraint and moderation in the face of extreme passions, actions, desires, and so on. That sounds all right, but there's a problem, since what is extreme in certain circumstances might be moderate in others.
Denouncing your teacher when she announces a pop quiz? Not temperate. Denouncing someone who is stealing puppies from children? Pretty temperate. As you can see, temperance is an unstable and often subjective idea that never corresponds to exactly the same thing (unlike, say, virginity—back in the LGBTQ-unfriendly days of Spenser, there was really only one way to be a virgin); there are lots of different ways to be temperate. However, we can think about Guyon himself as working through that instability and embodying not simply perfect temperance, but the challenge of applying temperance in various different contexts.
Sometimes, for example in the Castle of Alma (see Alma), temperance involves saying yes and showing curiosity. Other times, for example with Phaedria (see Phaedria), temperance involves saying no way and leaving pronto; it's no accident that in the book exploring the problem of temperance, there's literally a character named Occasion (see Furor and Occasion). The best definition of temperance we get in the text comes from the Palmer who says "But temeraunce… with golden squire/ Betwixt them both can measure out a mean,/ Nether to melt in pleasures whott desire,/ Nor frye in hartlesse greife…" (II.i.57).
Guyon's heroism has been called into question in two ways. The first way is to suggest that if Guyon is a hero of temperance, that doesn't make him particularly heroic. I mean, think about it: we want heroes/heroines to valiantly crush villains, achieve fame and glory, and sweep their man or woman off their feet. All these things require a certain amount of passion and emotion, both things that temperance seeks to avoid. If we think about Guyon in particular, there's definitely some truth to the fact that he's pretty low-action for a hero, compared even to Redcrosse.
Guyon rarely fights anyone. He usually just talks to them (like Mammon) and even in the great epic climax of Book 2, in the Bower of Bliss, Guyon just snatches Acrasia up in a net—not exactly Dragon-slaying level epic. There's no easy answer, but we might ask whether Spenser is trying to refashion the definition of heroism, and to suggest that not slaying anybody might be even more heroic. What do you think?
The other way in which Guyon's heroism is doubted is Guyon's final choice to destroy the Bower of Bliss after capturing Acrasia. When he destroys the Bower, Guyon is described as having "rigor pitilesse" and we hear about "the tempest of his wrathfulness" (II.xii.83). This language does not make Guyon sound like the most temperate guy, and one could even go as far as to say, he sounds downright extreme: No pity? Total wrath?
So, has his whole attempt throughout Book 2 to be temperate been just a big failure? Is true temperance impossible? Or, are we back to the problem of what temperance means, and in the face of everything bad the Bower of Bliss stands for (check out Images, Allegory, Symbols), is being wrathful actually temperate? One thing's for sure, Spenser succeeded in producing a character that challenges his reader to examine their own beliefs and expectations.