Mushroom is part of this narrative set-up. He is a court jester who served primarily with King Viserys I and Queen Rhaenyra, though he also spent some time with Rhaenyra’s rival King Aegon II. Archmaester Gyldayn tells his readers that he has two sources written by eyewitnesses to the civil war called the Dance of the Dragons; a relatively somber history from a cleric called Septon Eustace, who was a supporter of Aegon II, and the Testimony of Mushroom, an account told by Mushroom – a supporter of Rhaenyra – to an unnamed scribe years later which revels in salacious detail and always includes the most shocking, vulgar, or violent version of every story.
During the part of the novel that was adapted into season 1 of House of the Dragon, Mushroom’s main role is as an historical source that disagrees with Septon Eustace and that occasionally provides intimate details, like claiming he found Rhaenyra and Harwin Strong in bed together one morning, for example. The only way the television adaptation could follow the pretend-history format would be to do some kind of documentary, which of course would not work in a Westerosi setting (not unless we want to jump very far forward into Westeros’ future!) so the TV writers needed to actually show intimate acts and secret meetings directly to the audience, and they did not need a narrator-character to walk in on anyone.
When it comes to Mushroom’s actual versions of events, the television adaptation has selected some incidents where they want to follow the Mushroom version, and others where they have gone with a different version of Westerosi history, or even more often, a slightly different story all together. With a book written in this format, reporting rumors and gossip and contradictory versions of events, the TV writers have a lot of freedom to show scenes that are different to anything in the book, on the basis that the book’s eyewitness characters were not there or were lying or mis-remembering things.
They follow Mushroom’s version of the last dinner Viserys has with his whole family before his death almost exactly, for example. They cleverly half-follow Mushroom’s version of what happened to Laenor Velaryon and Qarl Correy; Mushroom’s version becomes what people believed happened (Daemon had them both killed), while what really happened (they faked their deaths and ran away) is a secret. But the television show goes for a completely different story than Mushroom when it comes to who arranged for the fire that killed Lyonel and Harwin Strong, as Mushroom claims it was Corlys Velaryon, while “others” suggest it was Larys Strong, who is the culprit in the TV version. Rather than going for any one source as being the only reliable one, or the source that gives us the truth, the writers have decided that each source has bits and pieces that are true and things that aren’t, and things that are half-true – which is almost certainly the case for most real histories.
It is a shame that there was not room for Mushroom in season 1, because as a jester, he is able to say things that no one else can say and his role is specifically to be funny, offering an opportunity for a bit more comic relief in a fairly dark show. According to his own history, Mushroom was the only person who could still make Viserys laugh during his last days, something that might have brightened that rather grim episode of season 1.
On the other hand, there was a lot going on in season 1 and a lot of characters to introduce to the audience, so without the need for the pretend-history framing device, we can see why he was left out. Scenes like Viserys’ death bed might also have been less intimate and less grimly dramatic if there had been a jester coming in and out and telling jokes. Going forward though, we would really like to see Mushroom brought in for season 2 and beyond, especially as he starts to play a bigger role in the actual plot itself, beyond just being a narrator, witness, and source of information.