- The Sword of Exile. It doesn't just kill you, it erases your very existence, and everyone's memories of you disappear. Essentially, if it had retroactive erasure as well, it would literally wipe every trace of you out of existence, but thankfully, your deeds themselves are not erased.
- The astral drops exist in some kind of limbo. There's nothing on this place except for the astral drop, who is alone, can experience feelings like anyone else and... she's trapped there unless the Guardian that created her takes her out of there.
- The astral drops probably have it worse in the cartoon, even though they're not sentient. They come into existence for a while, and after they're not needed they're made to go "poof". As if they never existed in the first place. Kinda sad really...
- Similarly, think of how Elyon was trapped alone in a jewel for the majority of season 2—from the beginning of summer (i.e. June) to the middle of December, provided they're following the typical American school year. Of course, she picked up some company in R is for Relentless, but that still means she was stuck there alone for around four months. It's amazing she didn't go stir crazy!
- Matt's first transformation into Shagon.
- Similarly, Mr. Huggles first transformation into Kor.
- In "Z is for Zenith", W.I.T.C.H. were close to losing their humanity. They would have remained in their super powered state, if it weren't for their loved ones.
- Cedric. Imagine a Consummate Liar so good with words and cunning that he can turn someone against their best friend with a single talk backed by a bit of carefully selected and presented truth, give him the ability to change his looks at will and disguise himself through non-magical means (redundant? No, it allows him to bring with him an ogre that can't disguise themselves with magic), and imagine what it would be to have him as an enemy
- Almost forgot: those above are not his only skills. He can fire energy blasts and Eye Beams, cast various spells (and is competent enough that he could teach Elyon to use hers and make her more than a match for all the Guardians in a couple weeks), and when he's after you he can track you down everywhere and anywhere, as shown when he hunted down Elias Van Dahl in the seventeenth century.
- With the description above, you could think that locking him in a form, taking away all his magic and knowing exactly who he is and that he's an enemy is enough to stop him. The Guardians thought so, and so did Matt. Then, in the Book of Elements arc, Cedric disabused them of this notion by tricking Matt into trying to open the Book, and getting sucked into it, by shouting at him to not come close to it when Matt saw the book embedded in a wall and got curious and then leaving the room with a perfectly believable excuse And he was improvising. Now you see why Orube's reaction at first seeing him on Earth was fear, don't you?
- Prince Phobos is a sadistic, powerhungry, and vainglorious madman who only cares about acquiring magical power. He will crush anyone who stands in his way, even if they are his own family. He takes great glee in manipulating and fooling his sister Elyon with his Faux Affably Evil demeanour until her power has reached its peak. And when the charade is up, Phobos mocks his own sister's naivety and has no problem binding her to a throne and zapping her of her magic. The only thing scarier than his ruthlessness and lack of empathy, is his short temper, and his habit of severely punishing those who fail or betray him.
- What's even scarier is that Phobos is still out there. While he is still floating powerless in an endless void, he is very resourceful. He already escaped once from prison while powerless by harnessing his hatred until he managed to find a spark of power and used it to switch minds with Endarno. Given enough time and hatred(which he has tons of) he'll definitely find a way to return. What's also scary is how his legacy will affect Elyon and future generations of Metamoorian royalty. Elyon and her subjects will most probably be somewhat paranoid that one of her future children will be evil, especially if she gives birth to a son who is the oldest and has magic like his uncle. No doubt there will be many Escanor princes in the future who will be scrutinized heavily to make sure they don't turn out to be another Phobos.
- Nerissa is even worse than Phobos. A former Guardian of the Veil and original owner of the Heart of Kandracar, Nerissa's desire for power corrupted her, leading the Oracle to strip her of the Heart. In retaliation, Nerissa murders her best friend and fellow Guardian Cassady, and is imprisoned in a tomb. Years later, she escapes (the reason different in the comics and animated series) and vows revenge on everyone. She appears as a hideous, scarred old hag, just as manipulative and amoral as Phobos, and to hell with anyone who gets in her way. She is a horrifying master of the Batman Gambit and the Xanatos Gambit, manipulating others for years to ensure she gets what she wants.
- Made worse in the animated series. Perhaps her most vile action was murdering the Mage and posing as her, before having sex with Julian to give birth to Caleb, wanting to have the perfect child to serve her during her plan for universal domination.
- Being a Guardian can be extremely nightmarish. The girls have faced death multiple times, and Cassidy did die. Who knows how many Guardians died before her? Not to mention they don't even get a guidebook or anything on how their powers work, they just get thrown into battle and have to figure out everything by themselves. And for someone who's supposed to protect everyone in the universe, the Oracle can be downright evil. It's a very good thing Yan Lin took over, as she's much more sympathetic and understanding.
- Even worse, a Guardian getting murderously angry. There was a glimpse early on, when an Imagine Spot showed Taranee setting Elyon's home on fire in a fit of rage (and it's strongly implied it came directly from her mind-so she had considered burning Elyon alive. Good thing she was chosen specifically because she would never abuse her power), but near the end of the Trials of the Oracle arc Will snaps, and a Gory Discretion Shot later we're shown Will has calmed down-but not before doing something that left Phobos terrified of her. And she was mentally broken and exhausted. No wonder that, when they met again after Will had recovered, Phobos was terrified when she demanded the others let her finish him off-and with good reasons, as she destroyed his soul.
- Original troper here. To add on to what you said, a Guardian doesn't even have to be murderously angry just mildly frustrated or upset, like Irma was with Martin back in issue #1. She told him to disappear and he did for several seconds. Earlier in the issue Cornelia called Lillian a toad and she croaked. In the Ludmoore arc when the girls couldn't get onto the bus to the spa, Will said, "I'm so frustrated I could explode!" Right after that, all four of the the bus's tires popped. Things also happen when a Guardian is severely depressed, like again in the Ludmoore arc when Will was so depressed after what happened to Matt she caused a power surge, and I believe a blackout but I'm not a hundred percent sure in her school. Now the real question is why the girls never bother to explore the true potential of their powers or to ask the Oracle about their secondary powers, or why Will didn't use the Heart to get Matt out of the book.
- The Light of Meridian is so powerful she can defeat all five Guardians of Kandrakar (though maybe Guardians who got their New Power form can beat her) and that's without the Crown of Light. Imagine if another generation of Guardians had to fight an evil Light of Meridian (can someone please write a fanfic about this?) Those poor girls wouldn't stand a chance!
- The marshes of the world of Arkhanta are inhabitated by banshee, who will have to grant three wishes to anyone who manages to capture one. Doesn't seem too bad... Until you realize there's people who goes in the marshes to temporarily enslave them.
- The banshee will murder anyone who enters their territory. They have good reasons, but what if someone completely innocent stumble in their territory by accident?
- Ari of Arkhanta went and captured Yua, the most powerful of them all (enough to be a low-level Reality Warper once she could access her magic to grant wishes). The first wish was for the Scarlet Citadel, an immense fortress to live with his son, and the second was for immense wealth to provide for him, and she granted them with no trouble. Then he wished for her to grant all his future wishes-and she had to grant that too. No wonder Yua twisted one of his wishes in such a way to leave him powerless before people they thought would kill him, or that she kidnapped his son the moment the Guardians freed her.
Nightmare Fuel / W.I.T.C.H.