The Testimony of Mushroom
The Testimony of Mushroom is an account by the court jester Mushroom, about the years he spent at court during the reigns of Viserys I Targaryen, Aegon II Targaryen, Rhaenyra Targaryen, and Aegon III Targaryen.
As Mushroom was the court fool and a dwarf, people believed him to be a lackwit. This caused the highborns to speak freely around him. Mushroom's testimony was written down by an unknown writer. The account is filled with Mushroom's tales of plots, murders, trysts, and debaucheries, amongst other things. The stories are in the most explicit detail.
Septon Eustace has written an account, The Reign of King Viserys, First of His Name, and the Dance of the Dragons That Came After, covering many of the same events that are described in Mushroom's account, and while often the two disagree on how events occurred, at times they do agree.
Poison!? He didn't die of poison, he died in his sleep!