X-Men 101: #34 - CASUALTIES

After battling the Marauders, Angel lost his wings, Nightcrawler was placed in a coma, Colossus became paralyzed and briefly stuck in his armored form, and Shadowcat was gradually "phasing" herself out of existence.
(Uncanny X-Men #212)

X-Men 101: #33 - MUTANT MASSACRE

The Morlocks, outcast mutants inhabiting New York City's sewers, were practically wiped out by Mr. Sinister's Marauders. Sinister believed the Morlocks to be scientifically useless in his quest for global mutant domination.
(Uncanny X-Men #210-#213)

X-Men 101: #32 - MADDIE ABOUT YOU

Cyclops' first wife, Madelyne Pryor, was a clone of then-believed-dead Jean Grey. She was created by Mr. Sinister to meet Cyclops and ultimately sire a mutant child that sinister believed would have powers vast enough to assist him in Apocalypse's destruction.
(Uncanny X-Men #241)

X-Men 101: #31 - WWII WOLVIE

Wolverine fought alongside Captain America in Madripoor during World War II.
(Uncanny X-Men #268)

X-Men 101: #30 - AMERICA CONQUERED

In an alternate future called "Days of Future Past," the Sentinels had conquered the United States! They'd killed most of the X-Men, Avengers, Fantastic Four and others, and threatened to conquer the world.
(Uncanny X-Men #141-#142)

X-Men 101: #29 - DON'T TOUCH

Rogue's super-strength, invulnerability and flight powers don't really belong to her. When Rogue was a bad guy, she maintained contact with Ms. Marvel too long, and Rogue's mutant power permanently stole Marvel's powers.
(Avengers Annual #10)

X-Men 101: #28 - SNIKT!

When Wolverine pops his claws from their sheath inside his arm, the claws actually pierce the skin on the top of his hands. His healing factor heals the laceration almost instantly.

X-Men 101: #27 - HODGE PODGE

Cameron Hodge was hired as X-Factor's original P.R.guy. He turned out to be a mutant-hater who led the terrorist group the Right, and eventually set up shop in the mutant-discriminatory country of Genosha.
(X-Factor #1, X-Factor #17)

X-Men 101: #26 - ANTI-X-MEN X-MEN

The first X-Factor roster was the five original X-Men who took advantage of public anti-mutant sentiment by posing as mutant hunters (they actually located and protected mutants). In their costumed identities they called themselves the X-Terminators.
(X-Factor #1)

X-Men 101: #25 - FULL CREDIT

Not only is Professor Xavier's School for Gifted Youngster's a cover for Xavier to teach his pupils how to use their mutant powers, but it's also a real school that gives a high school and college education.
(Uncanny X-Men #7)

X-Men 101: #24 - BLUE BOY

Beast wasn't always a blue furry guy. He started out as a human with abnormally large hands and feet, and later ingested an experimental serum that accelerated his mutation, causing grey fur to grow all over his body, his canines to grow and his already superhuman abilities to increase. His grey fur soon turned blue.
(Amazing Adventures #11)

X-Men 101: #23 - STOP THIEF

The first time Professor X met Storm, she was a young thief in Cairo who picked his pocket. He would return years later to recruit her to his new X-Men Team.
(Uncanny X-Men #117)

X-Men 101: #22 - STEEL YOUR BREATH AWAY

In his armored form, Colossus doesn't need to breathe. However, it is believed he could not survive long in a vacuum.
(Uncanny X-Men #150

X-Men 101: #21 - PEOPLE FOOD

For all her genetic schooling, Moira MacTaggert couldn't help her son Proteus. A mutant who can alter reality, Proteus needed human hosts to survive. On a rampage, he'd killed several people, including his father. But Proteus ultimately succumbed to his one weakness: metal, in the form of Colossus' mighty fists.
(Uncanny X-Men #125-#128)

X-Men 101: #20 - SHE'S ALIVE

Jean Grey was not the original Phoenix. When crash-landing from space, a cosmic entity took her place and left her in a cocoon at the bottom of New York's Jamaica Bay. She lay there for years until the Avengers discovered the cocoon, and the Fantastic Four revived her.
(Uncanny X-Men #101, Avengers #263, Fantastic Four #286)

X-Men 101: #19 - PROF BRAINIAC

Charles Xavier entered college at age 16, and earned a bachelor's degree in biology from New York's Bard College (he graduated in two years time), a master's in both genetics and biophysics from England's Oxford University, a Ph.D. in anthropology from New York's Columbia University, a Ph.D. in psychiatry from Oxford and an M.D. from Oxford.
(Official Handbook of the Marvel Universe #8)

X-Men 101: #18 - RED DAWN

Erik the Red is never what he seems. The first "Erik" was Cyclops wearing a disguise to foil Mesmero, Magneto and their Demi-men; the second was a Shi'ar agent named Shakari who was ordered to kill Lilandra; and the third was Magneto wearing a disguise to expose Gambit's past crimes.
(Uncanny X-Men #49-#52, #105, #350)

X-Men 101: #17 - POWER STRUGGLE

When Cyclops wished to lead the X-Men after a long absence, then-leader Storm offered to duel him for the position. The powerless Storm Beat him, and Cyclops left the team altogether.
(Uncanny X-Men #201)

X-Men 101: #16 - FIRST BLOOD

Thunderbird was the first full-fledged X-Man to die in the line of duty, trying to stop Count Nefaria from escaping. (Changeling, who died years earlier posing as Professor X, was named an Honorary X-Man after the fact.)
(Uncanny X-Men #95)

X-Men 101: #15 - DADDY DEADLY

Magneto is Quicksilver and Scarlet Witch's father. Though the three of them were all part of the original Brotherhood of Evil Mutants, none of them would find out the truth until much later.
(Vision and Scarlet Witch (first mini-series) #4)

X-Men 101: #14 - TIME GIRL

While trying to save Captain Britain from a time anomaly, Rachel Summers was hurled into the far future and became Mother Askani, the leader of a rebellion against Apocalypse. There she brought young Cable to the future, where he'd be trained to fight.
(Excalibur #75, The Adventures of Cyclops and Phoenix #1)

X-Men 101: #13 - WOLVERINE'S KID

Wolverine agreed to take care of a young Japanese girl named Amiko at the request of her dying mother. The girl is presently being watched over by Logan'y ally, Yukio.
(Uncanny X-Men #181)

X-Men 101: #12 - PROFESSOR MAGNETO

When Xavier left Earth with the Shi'ar to heal injuries inflected on him by an anti-mutant mob, he asked Magneto to run the school for him. Magneto did so under the name, Michael Xavier, but eventually left, unable to convince the New Mutants to follow his points-of-view.
(Uncanny X-Men #200, New Mutants #75)

X-Men 101: #11 - BAD GIRL

Before she joined the X-Men, Rogue was a member of Mystiques New Brotherhood of Evil Mutants. She came to Professor X seeking his aid with controlling her powers.
(Avengers Annual #10, Uncanny X-Men #158, #171)

X-Men 101: #10 - CAMERA SHY

After their battle with the Adversary, the X-Men were saved by the celestial being called Roma, who gave the X-Men the ability to not be detected by any mechanical or magical devices. Since then, the ability has faded away.
(Uncanny X-Men #227)

X-Men 101: #9 - ETERNAL BALL

Cannonball once apparently died and returned to life, and was therefore assumed to be an "External," a rare mutant who is able to live forever.
(X-Force #7)

X-Men 101: #8 - HUMAN X-MEN

Some X-Men aren't mutants. Mimic gained his power to duplicate others' powers after accidentally breathing in a strange gas in his father's lab, and Longshot is a genetically engineered humanoid from another dimension.
(Uncanny X-Men #19, Longshot #1-#6)

X-Men 101: #7 - CHUCKIE'S DEAD!

Xavier once had a shapeshifter named Changeling pretend to be him while the Professor secretly prepared for an alien invasion by the Z'Nox. When the "fake" Xavier died in battle, the X-Men even held a funeral. The genuine article returned a short time later.
(Uncanny X-Men #42)

X-Men 101: #6 - HEAD CASE

Cyclops can't turn off his optic blasts. When he was young, Cyclops was thrown from a burning plane and suffered a head injury upon landing, damaging the part of his brain that would've controlled his mutant powers.
(The Marvel Saga #4)

X-Men 101: #5 - POWER FAILURE

Brother's Cyclops and Havok's mutant powers are both capable of incredible destruction, but for unknown reasons, their powers can't affect each other.
(X-Factor #61)

X-Men 101: #4 - DIS-ORIENTING

Psylocke was once Caucasian (British, actually). Her mind was transferred into the body of an Asian assassin named Revanche, whose mind was transferred into Psylocke's. Dying from the Legacy Virus, Revanche had herself killed by Matsu'o Tsurayaba.
(Uncanny X-Men # 257, X-Men #22, #31)

X-Men 101: #3 - PHOENIX LITE

Phoenix was not supposed to die at the conclusion of Uncanny X-Men #137. The creators originally intended only for Jean Grey to be stripped of her powers, but the powers that be felt that she deserved a harsher fate.
(Phoenix: The Untold Story)

X-Men 101: #2 - FIRST OF SECOND

Nightcrawler was the first of the New X-Men team recruited by Professor X. He was about to be killed by a mob in his native Germany before the Prof stepped in.
(Giant-Size X-Men #1)

X-Men 101: #1 - XAVIER CLONED

Charles Xavier isn't in his original body. It was destroyed when a Brood Queen "hatched" from it, and alien technology put his brain into a cloned body that could walk. His new legs would later be crushed in a fight with the shadow king.
(Uncanny X-Men #167, #280)