Alternate Identity Amnesia: One-sided. A person's real-world self doesn't share memories with their Shadow, which is a good thing for the Thieves as it means nothing they do in the Metaverse risks exposing them. A Shadow is fully aware of their real-world self's memories, though.
And That's Terrible: Whenever you catch a glimpse of the Targets' depravity in full-force, at least one of your party members will always comment upon how utterly horrible said target is and make it perfectly clear that their heart must be stolen, no matter what.
The Atoner: After you change their hearts, they gain the desire to make amends for their sins.
Bring It: The Palace bosses (with the exception of Shadow Futaba) react to their calling cards in this manner: the screen flickers, revealing the Target's true self, who taunts the Phantom Thieves to steal their treasure if they dare, before the Palace's security rating rockets up to 99.
Card-Carrying Villain: Expounded upon more in Hate Sink below, but both the Targets in the real world and their Shadows often present themselves as thoroughly unpleasant people with little shame or remorse for how they conduct themselves.
Defeat Means Playable: For a few Mementos Targets, defeating them bestows a key item that unlocks their corresponding Persona for fusion.
Evil Is Petty: All the Targets are unhealthily petty to absurd degrees, most of them not even trying to hide it while in the real world.
Fate Worse than Death: The Phantom Thieves aim to change the hearts of their Targets as killing them would not solve anything and their Target will still be remember as a hero of some kind. Following the success of their mission, the Targets are arrested and their crimes are exposed, forever ruining their reputation.
Females Are More Innocent: As noted on the main page, the two major female targets are nowhere near as twisted as the male targets. Futaba in particular is a special case: you're stealing her heart not to reform her, but to prevent her from committing suicide. Averted for the women you target in Mementos, however, who are just as wicked as the men - though the women are sharply outnumbered.
Freudian Excuse: Several of the Mementos Targets will reveal, after you defeat them, that they too were victimized by the system, and figured that if they couldn't beat the corrupt establishment they might as well join it.
Freudian Excuse is No Excuse: While many of the targets have their personal tragedies, the thieves point out that this doesn't justify what they put their victims through.
Hate Sink: Justified in the case of the Shadows themselves—since Shadows are the darkest parts of humanity given life, it's expected that the Targets' Shadows would be unashamedly evil (or in the case of the Mementos Targets, generally unpleasant). However, the story goes out of its way to present the mass majority of the Targets in the real world as thoroughly reprehensible people as well, allowing the player to feel less guilt when it comes to stealing their heart away.
Heel–Face Brainwashing: Stealing their Treasures removes their distorted desires and gives them an intense desire to atone for their sins.
Heel Realization: The response of most Targets to having their Treasure stolen is a sudden feeling of remorse and actively attempting to repent for their crimes. The only exception is Shido who prefers to commit suicide rather than be changed... though even then, after failing, he too tries to repent for his actions.
It's All About Me: Most of the Targets are generally selfish people who are willing to do anything to fulfill their own desires, from harming their own family members to committing murder.
Kick the Dog: All of them have their moments of doing evil things for the sake of sadism.
Laser-Guided Karma: Each of the main Targets gets a dose of it, most often during their boss fight:
Kamoshida, who used his past glories as an excuse to abuse the students under his care, is stripped of the representations of these trophies over the course of his Shadow's boss fight, leaving him as the pathetic monster he is deep down. And after the boss fight, he's cornered on a balcony by a very pissed off Ann, who takes the chance to point out that what he's feeling is probably how Shiho felt when she jumped off the school's roof.
Madarame stole the artwork his students created to pass it off as his own. During the fight against his Shadow, it covers party members in ink in order to weaken them and make them vulnerable to his attacks. If the fight goes on long enough, you get the opportunity to steal his own trick and use it against him.
Kaneshiro, who lured in students with the promise of a "part-time job" in order to Blackmail them, is lured in by the Thieves giving up a valuable item in order to distract him from the fight, letting the Thieves wail on him without worry.
The Sphinx, the representation of Futaba's guilt over her mother's death, is bought down when Futaba decides to stop feeling guilty and fights back.
Kunikazu, who espoused betrayal as necessary in order to get ahead in the world and relied on always having disposable workers, eventually runs out of robots to throw at the Thieves during his boss fight, and is ultimately betrayed not only by his own daughter but by The Conspiracy, who set him up to die so that they can frame the Thieves.
Shadow Sae, who spent the entire dungeon claiming that she'd fight "fair and square" only to keep rigging games in her favor, is forced into an actual fair fight after being exposed one too many times and ultimately loses.
Goro Akechi, the personal assassin of the Big Bad and a traitor to the Phantom Thieves, ultimately dies saving the Thieves when Shido's cognition of him turns on him for his failure and reveals that he was always meant to be disposed of in the end just like Goro did for everyone else who could potentially stand in Shido's way.
Furthermore: having done everything he did in order to receive affirmation and praise, his ultimate deed of glory takes place where nobody could see it, under circumstances that mean nobody besides the other Thieves will ever know that in the end he was truly a hero.
Masayoshi Shido, a Corrupt Politician who crushed the lives of many innocents for reasons ranging from power to pettiness, is ultimately brought down by the Phantom Thieves, of whom many of which, particularly the Protagonist, are among the people whose lives he tried to ruin. Not to mention it was his attempts to ruin their lives that bought the Thieves' attention to The Conspiracy in the first place.
Yaldabaoth, a malevolent god who claimed to represent the voice of the masses, is defeated when the masses ultimately support the Phantom Thieves, allowing Joker to summon Satanael.
MacGuffin: Each Target has a Treasure that the Thieves need to steal in order to change their hearts.
Motive Rant: Since the Shadows are born from the Targets' repressed issues, they'll often go on about what led their hosts to become this way.
My God, What Have I Done?: When the Target's Treasure is stolen and their Shadow beaten, the Target's heart will be unable to handle the guilt and they will immediately confess and beg to be punished.
Never My Fault: Part of their MO when confronted is to blame their victims or society.
Nice Job Fixing It, Villain!: The Targets' tendencies to be so remorselessly cruel to unnecessary lengths only bolsters the Phantom Thieves' resolve to steal their hearts.
Obviously Evil: Their mere appearance already shows that these people are assholes who will trample on anyone for their own benefits. In fact, some of them do not bother hiding their true nature to others.
One Steve Limit: Beelzebub, Satan, and Lucifer are recurring characters in Shin Megami Tensei and also show up as individual Personas here, so the Shadows that represent Gluttony, Wrath, and Pride use alternative demon names instead.
One-Winged Angel: When confronted, the Shadow Selves of each Target transform to combat the Thieves. Those mainly affiliated with the Conspiracy have unique forms based on the below trope, while the Mementos Targets often transform into a Shadow which Joker can use, or as a Mook in most cases.
Seven Deadly Sins: The main motif of all of the major Palaces and their Shadows. Six of the regular seven are embodied by the owners of each Palace, along with two non-traditional ones (Emptiness and Vanity, alternatives / counterparts for Sloth and Pride). Sloth is a special case: the Mementos dungeon is its representative "Palace", and the people of Tokyo as a whole embody the sin, which is shown during the endgame when the Greater-Scope Villain begins to enact his plan.
Single-Issue Psychology: A Treasure is a distilled manifestation of what triggered the Targets' internal distortion. The majority of the Targets' distortions can be traced back to a single reaction they'd gained from a simple object that'd mean virtually nothing to anyone else.
Society Is to Blame: Many of the Targets in Mementos and all of the Palaces' rulers will at one point or another will blame society for the way they turned out, whether it's the public's mistreatment toward the poor (Ichiryuusai Madarame, Junya Kaneshiro, and Kunikazu Okumura), stress due to people's increasing expectations of them (Suguru Kamoshida), undeserving blame for those looking for a scapegoat to misfortune (Futaba Sakura), sexist discrimination in a male-dominated environment (Sae Niijima), or believing that they need to preserve themselves and a chosen few in a continuously declining society (Masayoshi Shido). The Phantom Thieves will usually retort by pointing out that they are still fully responsible for their own actions. Granted, all of them do have a point to varying degrees, which actually becomes a major plot point as the story progresses.
Unnamed Parent: Averted. Despite the fact that most Shadows are referred to by their last names, including those who are parents of other characters (for example, Mitsuyo Togo is called "Hifumi's mother" in her dialogue boxes), their first names are briefly mentioned, and are necessary knowledge to take on their Shadows.
Villain Ball: The Targets tend to hide their darker sides well enough from the rest of society, but when they lash out, they all prove themselves to be so unrepentant and malicious that it simply gives the Thieves more of a motivation to steal their hearts away. A particularly egregious moment comes along when Madarame's Shadow manages to fool the Thieves into stealing a fake Treasure... only to confront them a few moments later with the real Treasure just to flaunt it in their faces—and the ensuing exchange between him and Yusuke only bolsters Yusuke's resolve, culminating in the destruction of Madarame's Palace.
Villain Has a Point: While the Targets are ultimately responsible for their own selfish choices, it is true that society's flaws are partly responsible for influencing those choices to various degrees given how rigid Japanese society is. In fact, it becomes a major plot point to where it is tied to the final boss and embodies the Sloth of the people of Tokyo.
Villain with Good Publicity: Several of the better-known Targets are able to get away with what they do because of their reputations or the results they bring.
Would Hurt a Child: Many of them have no problem hurting or exploiting teenagers, even if said teenager is their own child.