Sham

Shamus Yes ap Soorap, an utterly incompetent apprentice doctor on the Medes who inadvertently gets involved with the Shroakes.

Distressed Dude: During his time with Robalson & later on the Island.
The Ditz: At first, sort of. Not so much as of the introduction of the Shroakes.

Misery Builds Character: Played pretty straight; after everything that happens, he becomes outspoken & willing to stand up for hismelf & others.
Resigned to the Call: During the last third or so of the book.

Captain Naphi

Abacat Naphi, an elegant & taciturn moletrain captain who just wants to kill Mocker-Jack.

Animal Nemesis: Mocker-Jack. This gets unsettling & disturbing once she becomes convinced it reciprocates.
"I'm his philosophy..."
Berserk Button: Call Mocker-Jack yellow one more time.
Broken Ace: She's supposedly one of the best molers alive, but the more screentime she gets, the more obvious it becomes that she is far from psychologically healthy.

Mask of Sanity: It's implied she's been crazy the whole time, & her "sudden" breakdown at the end was just dropping the act.
Not So Stoic: She quickly stops even trying to seem like The Stoic after the mutiny.

Savvy Guy, Energetic Girl: Gender-inverted with Mr. Mbenday; she is somber and stoic, while he is very energetic.
Terse Talker: Usually, unless she's making a speech.
Two Guys and a Girl: With Mbenday & Brownall.

Caldera Shroake, the elder of the two Shroake siblings, as well as the de facto leader.

Brother–Sister Team: With Dero.
Doom Magnet: Justified, because the villains pursuing her do so because they believe her & Dero can lead them to riches or information.
Goal in Life: Hers & Dero's is to finish their parents' quest. They will go to any lengths necessary to do this.

Caldero "Dero" Shroake, the younger of the two Shroake siblings.

Brother–Sister Team: With Caldera.
Doom Magnet: Justified, because the villains pursuing him do so because they believe him & Caldera can lead them to riches or information.
Goal in Life: His & Caldera's is to finish their parents' quest. They will go to any lengths necessary to do this.

Boyza go Mbenday, the first mate of the Medes and the one to start the mutiny against Naphi.

Good is Not Nice: Despite being easily the kindest out of the Medes officers, it was Mbenday who started the mutiny.
Machete Mayhem: He chops up an alien monster with machete. One of the most badass scenes in the book.
Minored in Ass-Kicking: He is primarily a navigator, and for a lot of the book, doesn't seem to have any combat-related skills, especially compared to the short-tempered Brownall and the reknowned ace Naphi. However, come the battle with the Siller, he chops off several of its limbs with a machete.
The Navigator: And he's better at it than Naphi.
Rebel Leader: Averted. He starts the mutiny, but it's Vurinam who really gets everyone into it.
Savvy Guy, Energetic Girl: Gender-inverted with the other officers of the Medes. He is energetic and enthusiastic, while Naphi and Brownall are glum and somber.
Seriously Scruffy: Implied, and also justified, as he is the second-in-command to THE ace in this book's setting.
Sliding Scale of Leadership Responsibility: Generally fairly responsible, until he starts a mutiny which winds up throwing the whole train into disarray and unease, and also technically makes him the captain, a role for which he is completely unprepared (and that is definitely irresponsible).
Two Guys and a Girl: With Naphi and Brownall.
Unfit for Greatness: Is an awesome first mate, but impliedly not the best captain. Especially given who preceeded him in that position.