Uncanny X-Men #126 Oct 1979
"How Sharper than a Serpent's Tooth...!"
The X-Men’s private Blackbird jet blazes across Scotland’s moors in haste to reach Muir Isle.
Responding to Lorna Dane’s distress over the phone, the X-Men left in
such a rush that they could not even wait for the Beast to rejoin them.
Upon arriving at Muir, they split into small groups to search the facility. Colossus finds Alex, who has suited up as Havok.
Banshee and Cyclops find Lorna and the ravaged body of Angus MacWhirter. Storm finds Moira.

Cyclops finds Phoenix still dazed after a fight with Mutant X.
In a haze, she initially thinks Cyclops is Jason Wyngarde; Scott is disturbed when she calls out the name Jason.

The entire group convenes in Moira’s home. Jamie recounts the events that happened after Lorna’s call was cut short:
Mutant X first attacked Phoenix, but she drove him off. Afterwards, Jamie created a small army of duplicates to search the grounds.
When Mutant X then attacked Lorna, she also successfully repelled him but one of Jamie’s
duplicates came on the scene and the villain took him over, knocking Jamie for a loop.

Cyclops demands to know who Mutant X is and Moira reveals that he is her son.

Meanwhile, using the form of Madrox's doubles body, Mutant X has escaped to the nearby city
of Stornoway where he attempts to find a new body Jamie’s duplicate is almost spent.
He crosses paths with an unaware Jason Wyngarde, but is foiled by the latter man’s psychic defense mechanism.
Alas, the hapless Ferdie Duncan fares less well.

The next morning the X-Men including Phoenix, Havok, Polaris and Moira head to the mainland
while Jamie remains behind. They reason that their target will be headed towards a major town or city. As they split up,

Moira explains to Cyclops that she’s been attempting for years to rein in her son’s killer instinct with no success.
She further explains that he will be driven to seek more host bodies as he burns
through his victims and that his one weakness is any form of metal, which is toxic to him.

From a distance, Jason Wyngarde observes the team’s dispersal
and causes Jean to suddenly experience another vision of an 18th century life.
She's a Scottish noblewoman riding horseback on a hunt alongside her “betrothed” -- Jason.
Suddenly, the dogs bring their quarry down and when Jason clears them off, he offers Jean the knife in order to put down their quarry.
She initially accepts his offer but blanches when she realizes they’ve been
hunting a man playing the part of the stag - and Jason claims it was her own idea!
The shock reverts her back to reality and she finds a mummified corpse of one of Mutant X’s victims.

Wolverine has picked up Mutant X's scent. Ignoring the radio call concerning Jean’s find, he follows his nose to a policeman.
Impressed at how fast Wolverine saw through his new facade, Mutant X tries to
possess him only to recoil when he realizes his opponent’s his body is laced with metal.

Nightcrawler drives up just as Wolverine threatens to gut their enemy.
Mutant X, who now declares that he has renamed himself Proteus,
demonstrates his ability to warp and twist reality itself.
Wolverine's heightened senses make him especially susceptible to this form of attack.
He and Nightcrawler are nearly overwhelmed when Storm arrives to aid them.
Her attack distracts Proteus but he quickly turns gravity upside down on her, causing her crash her into the ground.
Injured and in danger of becoming Proteus's next host, she desperately tries to repel him with a massive gust of wind.
Yet he inexorably closes in on her.

Story by Chris Claremont and John Byrne. Art by John Byrne and Terry Austin.