PathFinder: TodHunter Moon, Book 1

People traveled to a distant location. Some people have gills. However, the only way to find out if you have them is to go into the water and "drown". If you find you can actually breathe, you have them. (One character near the end does.)

Septimus Heap and his family play roles here. The adventures are different than those in the previous series. The characters are now more mature, but they still have dragon adventures. (Why do I have such a hard time remembering the details?)

Fyre: Septimus Heap, Book Seven

In the final Septimus Heap book, there is some back and forth time travel, where Septimus sees himself. Before that, there are some weird experiences with the bumbling Heap brothers. They end up stealing a special ring. However, it turns out that it was the ring that "stole" them and was using them as a vessel for mischievousness. And speaking of vessels, we learn that Gin can occupy various bodies of animals and humans, with some being worse than others. The book concludes with some reverse alchemy where gold is turned in to lead.

Very few of the characters in this series take themselves seriously. The few that do stick out and contribute to the light tone.

Darke: Septimus Heap, Book Six

More adventures of the clan. There are dark dragons, and continued dark trickery? (Is this the one where they tricked the Gin to consume the dark thing or was that the previous.) There is some reluctant assumption of royalty and gradual moving into roles. The culmination is a spell that helps unbind darkness and create more balance in the world.

Syren: Septimus Heap, Book Five

The fifth Septimus Heap book continues on with adventures. Septimus is stranding on an island with his dragon. Alas, his dragon has an injured tail. He trails to heal it, but the dragon keeps biting it. He tries a "cat funnel" on the head. A girl sees them and later shows up as a long lost person. There is still a bit of time travel involved along with some adventures.

Queste: Septimus Heap, Book Four

More action. More misplaced time. More family conflicts. An interesting twist about being about to travel to a different place in time as long as something is left behind.

The Darke Toad: Septimus Heap, Book 1.5

Darke Toad is a short novella that fits in between the first two Septimus Heap books. I managed to read it after reading the second one. There is a toad.

Physik: Septimus Heap, Book Three

Dragons, shape-shifting cats, time travel and female Hanseatic traders all play a role in this third Septimus Heap book. There are also ghosts walking around and a rats that barely escape certain death by escaping on a dragon. There are also alchemist apprentices and other challenges.

And these are just the sideshows.

The main plot centers around Queen Etheldredda and her diabolical plot for immortality. That requires some harm to the main characters. But, of course they are not going to go down so easily.

Flyte: Septimus Heap, Book Two

Septimus Heap seeks the ability to fly. However, most of the book is occupied with the kidnap of Jenna. She is kidnapped by Septimus' older brother Simon who is jealous of him and his apprenticeship to the ExtraOrdinary wizard. Jenna is not a damsel in distress and uses things like a "chocolate spell" to help get out. There is plenty of sibling rivalry in a magical world. 

Magyk: Septimus Heap, Book One

Magyk is an interesting "fantasy comedy". The magicians and the custodians are in conflict. There are a few "orphan" children that end up playing key roles. One is identified as a princess. One is identified only by a military number, but later shown to be of magical origin. (Thanks in part due to an unintentional mix up.) There are also plenty of "magical" creatures, such as messenger rats.
The narrative was quick and compelling, and full of dry humor. I also loved the end where the other provided details of the fates of all the minor characters. I can think of many cases in other works where I have wondered how these events may have impacted this minor character. Here, the author seemed to have a lot of fun doing just that.