UNCANNY X-MEN #27: Re-enter the Mimic!

The Mimic joins the X-Men and things go bad, like, immediately.

UNCANNY X-MEN #25-26: The Power and the Pendant! / Holocaust!

The X-Men do battle with a gem-thief, a Mayan Serpent God, and their own drama!

UNCANNY X-MEN #24: The Plague of... the Locust!

The X-Men thwart the mutant insects of a disgraced university professor with delusions of grandeur!

 

UNCANNY X-MEN #23: To Save a City!

Will the X-Men accept Count Nefaria's offer to help ransom the city of Washington D.C.?

UNCANNY X-MEN #22: Divided -- We Fall!

The X-Men fall (dividedly) to five hired villains in the service of the dapper Count Nefaria!

UNCANNY X-MEN #21: From Whence Comes... Dominus?

The X-Men must defeat Lucifer and his world-conquering somethingorother!

UNCANNY X-MEN #20: I, Lucifer!

Ugh, it's freaking Lucifer again. Let's get this over with.

UNCANNY X-MEN #19: Lo! Now shall appear... The Mimic!

...And in this corner, hailing from New York City, featuring the combined power of all six X-Men... "The Mimic," Caaaaaaaalvin Rankiiiiiiiiiiin!!!

UNCANNY X-MEN #18: If Iceman Should Fail--!

Iceman must stand alone against the might of a returning Magneto, who will stop at nothing to birth his own race of mutant superslaves!

UNCANNY X-MEN #17: ...And None Shall Survive!

Still reeling from their battle with the Sentinels, the X-Men face a mysterious enemy who fells them one by one in their own home!

UNCANNY X-MEN #16: The Supreme Sacrifice!

The X-Men must discover a way to defeat the deadly Sentinels, or else mutantkind is doomed... and so is humankind. Basically it would be bad news for everybody.