Anniversary issues are meant to show great changes in the lives of the characters, and this being the first actual anniversary issue, it certainly lives up to the tradition.
First, I implore you to buy this issue. Why you wouldn't, I have no idea. Second, after reading this, refer back to issue #22 in the pages where Nightmare gives Emma a special gift.
Now, let's talk about what happened. Mondo took over the school as a horde of Black Tom Cassidy. All the kids, aside from the litluns and their friends, and Jubilee, were placed in an organic bubble, kept underwater and in tact mentally by Black Tom. After capturing Banshee and the White Queen, Tom tried killing the littler kids (read: Artie, Leech, andFranklin) along with Howard, Beverly, and Tana Nile, an extraterrestrial. But he was stopped short when Howard set him on fire and Man-Thing showed up to save them.
In order for Sean to help free the kids (or, rather, what he thought were the kids in the plant-covered estate), Tom said he must kill Emma Frost. He refused, so Tom made Emma start fighting him. The, as the only way she could save the children, she took control of Sean's mind and turned his power on against her. After that, Tom sliced Synch down the middle to reveal they were nothing but casks of the kids.
Tom talked of how he's planned this for months, perhaps since Generation X was first assembled. He took everything into account. Except Penance. The now revealed deaf girl sliced him straight down the middle, ultimatly killing Thomas Cassidy.
So, happy anniversary. Mondo turned on his classmates, was later killed by Bastion who kidnapped Jubilee before Mondo got to her, Black Tom got Emma supposedly killed for nothing then was destroyed himself, and Gateway showed himself for the last time at the academy. Bon Anniversaire.