* SugarWiki/AwesomeMusic: A textual version is Arthur's song in ''Grim Tuesday'', which won him [[spoiler: the Second Key]]. And it was just a song he made on a xylophone when he was a kid.
* CompleteMonster: [[ItsAllAboutMe Superior Saturday]], in a world with many sympathetic villains, is an out-and-out monster. Her method of disciplining her immortal subordinates is to turn them inside out and turn their blood into glass, essentially making them an organ jar for [[FateWorseThanDeath all eternity]] unless someone saves them. [[TheManBehindTheMan Being behind most schemes since the beginning of the series]], she releases a mind control virus; attempts to nuke a town; throws the Piper into Nothing to be dissolved, and blames his brother. DrivenByEnvy at feeling that she should have been favored during the creation of the Universe, Superior Saturday commits multiple unbelievably heinous acts to be the woman in charge.
* DesignatedVillain: For someone whose sin is Pride, Lord Sunday's sole shown (rather than exposited) motivation is to be left alone and for [[spoiler: the universe to continue existing]]. Despite the fact that his key's primary power is to override the other keys, he leaves the heroes alone and doesn't ever step in to hold him down until Arthur is on the verge of [[spoiler: destroying the entire universe]]. His section of the house is well-maintained with happy, productive residents and he refrains from doing any more than harming Arthur and bluffing him a bit when he needs to obtain the keys, even though most people would probably stoop to a bit of harm solely for spite's sake.
** He could been a little less cryptic and just have explained to Arthur '''exactly''' what the situation was, and could have avoided a lot of the bad stuff happening in the preceding books simply by taking an interest rather than considering it beneath him to get involved. Also, the way he parts the clouds on the underside of the Gardens purely to taunt Saturday absolutely screams pride.
* HarsherInHindsight: The main evidence that the book is set after it was written (2003-2010) is references to the pandemic that killed Arthur's biological parents, which caused an incredible number of deaths and resulted in the government passing laws authorizing the use of ''extreme'' measures to stop disease spread (such as nuking a hospital). The UsefulNotes/COVID19Pandemic fits the description given disturbingly well -- Australia, where Garth Nix lives, took notoriously harsh measures including closing internal borders, banning everyone (including citizens) from returning from countries experiencing major outbreaks, and banning gatherings of three or more people under threat of prison time.
* IKnewIt: Let's face it, [[spoiler:the Will turning into the Architect when it was completed]] was just obvious.
* WhatDoYouMeanItsNotDidactic: The [[HazardousWater Nothing-polluted rain]] in the Far Reaches, caused by too much mining of Nothing.
* WhatDoYouMeanItsNotSymbolic: ''Everywhere''. The series itself is named for a line from [[AsTheGoodBookSays the gospels]], and it just gets deeper from there. The Incomparable Gardens are a fairly obvious reference to the Garden of Eden for a start, and given that Lord Sunday's [[SevenDeadlySins sin]] is {{Pride}}, he could be interpreted as the equivalent to [[{{Satan}} Lucifer]]. Saturday's Tower, built with the intent of reaching the Gardens, calls to mind the TowerOfBabel. The Incomparable Gardens are also hosted on "Drasils", which is suspiciously similiar to the word "Yggdrasil", the World Tree of Norse mythology. Not to mention the Seven Deadly Sins and Seven Virtues from the Christian faith.