Fallen Prince: Skeeve's sojourn on Perv reveals that Aahz had been a wealthy, brilliant, insufferably-smug Big Pervect On Campus in his college days, right up until his widowed mother lost the family fortune on bad investments. Although offered a scholarship, Aahz was too proud to accept one, and quietly left school without a degree.
Freudian Excuse - Virtually all of Aahz's bad habits and vices can be traced back to specific events in his youth.
Guile Hero - The moment he opens his mouth, you're about to be conned.
Made of Iron - Superior muscle strength and very tough scales allow Pervects to shrug off glancing hits from swords and such. As well as allowing them to yank iron bars out of walls and other such party tricks.
Papa Wolf - Go ahead, threaten Skeeve in front of him. Or, you know, don't.
Parental Neglect - He admits to Skeeve that he mostly left his kids' upbringing to other people.
The Reptilians - Scaled, green, short, and strong as all get out, with pointed ears. Unlike typical Lizard Folk, he's also very, very intelligent and used to be a great magician. (And, you know, a hero.)
Badass Normal: Unfortunately, they hang out with so many Trolls, Pervects, and hyper-competent assassins and magicians that they tend to be overshadowed a lot.
Bodyguarding a Badass: Neither Guido nor Nunzio bear the slightest illusions that they'd be anything more than a speedbump if someone actually tried to assassinate Skeeve.
Hidden Depths: Both bodyguards are college-educated and highly experienced. Nunzio, especially, is a former schoolteacher and animal trainer, and displays knowledge of comic books, Broadway plays, and advanced economics.
The Mafia: They're nice guys, but they are legbreakers for the Mob.
Plot Allergy: Guido's allergy to garlic and fur becomes an inconvenience when Skeeve brings him along to Limbo, home dimension of both vampires and werewolves.
Dropped a Bridge on Him: Poor Roddy might have had a long and prosperous reign. But he died mysteriously and with very convenient timing. As it happens, he really did die mysteriously with convenient timing... of natural causes.
Prince and Pauper: King Roderick planned to use Skeeve's facility with disguise spells to take a permanent vacation.
Synchronization: To safeguard Possiltum, Skeeve tricks both of its monarchs into donning rings that link their lives, so neither can murder the other without killing themselves. It's nothing more than a con — as Queen Hemlock finds out when Roderick dies of natural causes and nothing happens.
Brawn Hilda: Resembles this trope so much that one of her wedding guests is overheard to remark that "it (the wedding) won't be over until she sings." Bunny is not amused.
Hidden Depths: Like most of the characters, there's a lot more to her, especially once you get to hear things from her POV.
Impossibly Tacky Clothes: The colors of Massha's clothing, hair and cosmetics clash virulently with one another. This trope also extends to her choice of decor for The Fun House and the trappings for her wedding.
Intimate Healing: She negates the Geek's state of extreme inebriation by smooching him. Apparently, she's had this effect on a lot of drunks.
The Nicknamer: Her default mode; examples include Hot Stuff, Dark and Deadly, Green and Scaly, and on one memorable occasion, Short and About To Become Extinct.
Obfuscating Vanity: Uses said fashion victim clothing, garish makeup, and loud, brash personality to hide her dependence on magical jewelry to do all her spellwork—and also her sensitivity and vulnerability thanks to being so overweight.
Sad Clown: Once you get past the irreverent jokes and naughty humor.
Synchronization - To safeguard Possiltum, Skeeve tricks both of its monarchs into donning rings that link their lives, so neither can murder the other without killing themselves. It's nothing more than a con — as Queen Hemlock finds out when Roderick dies of natural causes and nothing happens.
Fantastic Racism - His first profession is demon hunter, essentially meaning his job is essentially tracking and killing aliens for being aliens.
The Chew Toy - Gets conned out of nearly everything he owns, turned to stone, buried, dug up, dragooned into a mission he doesn't even faintly understand, marooned in an alien dimension, and locked into an employment contract barely a step above slavery. And it's hilarious.
Compressed Vice - It takes an absurdly short amount of time for being the head of a corporation to go to Skeeve's head.
Guile Hero - he gets better at it as he goes along. Makes sense, seeing as he started life as a thief.
Magnetic Hero - Most of the friends and allies tend to look to him as leader, though Aahz and Bunny can give him a run for the money, sometimes...
Nice Guy - He's not top of the heap in brains, brawn or magical power; he tends to end up as the leader because he's likeable.
Pop-Cultural Osmosis Failure - Virtually every other member of the cast casually spouts references to 20th century Earth media, while Skeeve has trouble with simple idioms. Initially explained by his native dimension of Klah being a backwater, this gets called into question in later books when fellow Klahds like Nunzio prove to have the Earthly cultural literacy that Skeeve lacks.
Trademark Favorite Food: Strawberry milkshakes ... at least, once he gets over his initial distaste because they look like pink mud.