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)