His troupe is just one of an estimated 850, with 10,000 members around Austria marauding through towns and villages over the Christmas period in "Krampuslauf" parades.
"We are spreading the tradition of scaring away evil spirits," Eigner told AFP as he donned his outfit before one such event in Schwadorf near Vienna.
"Just symbolically though of course," he said, resplendent in his shaggy Roman centurion-cum-zombie costume, animal bones dangling here and there.
It starts off innocently, with Santa -- or rather Saint Nicholas -- giving out sweets. But fear is in the air because soon come his satanic sidekicks, dozens of them.
Wave after wave bound in, stomping around a roaring fire that sends sparks into the night sky, clanging cow bells attached to their backs and brandishing whips and blazing red flares.
With heavy metal blaring, the several hundred spectators in the market town watch behind safety barriers as the demonic creatures prowl around menacingly, leering at the public.
But apart from one tearful little girl, everyone has fun. The monsters high-five with kids as they slope off back to their lair -- actually the local school -- to get changed.
"We are trying to make it look brutal but our whips are only made of horse hair," Eigner assures us. "People can hardly feel it if we hit them."
Black angels and orcs
It's a booming trend, with ever more groups springing up to satisfy a seemingly insatiable demand, and not just in Austria but in southern Germany and further afield too.
One of Austria's biggest parades, in Schladming south of Salzburg, involves some 800 monsters and attracts 8,000 spectators paying 12-15 euros ($14-18) per adult.
Yet, while it may be inspired by past customs, the phenomenon has moved and evolved far beyond its supposed origins in the remote valleys of the Alps.
Head-to-hoof in dark fur with horns, a tail and a lolling red tongue, from the 16th century Krampus traditionally appeared on December 5th, the eve of Saint Nicholas Day.
"Children would be tested on religious knowledge by Saint Nicholas. He would reward them but couldn't punish them. That was Krampus's job," ethnologist Helga Maria Wolf told AFP.
"Even into the 1960s, the pair would visit families on request," she said.
"Perchten" meanwhile, figures of good and evil whose origins are possibly pagan, would emerge in early January or in the carnival season before Lent, the Christian period of fasting.
Traditional Perchten processions still exist, such as in Gastein in western Austria where 140 creatures from mythology and legend "drive out winter" every four years.
But in recent decades, Krampus and Perchten have merged into hybrids, incorporating other influences from horror movies to heavy metal music, and appearing from early November onwards.
In Schwadorf there was Death himself and an assortment of witches, monks, red-faced Satans, black angels and other beasts resembling "Lord of the Rings" orcs.
Every Krampus season however, Austrian newspapers are full of stories about drunken young men dressed up as monsters causing injuries and mayhem.
In one such recent event in the town of Völkermarkt, police were called after at least six people were injured, reportedly after two rival Krampus groups clashed.
One therapist near Salzburg, Andrea Hammerer, runs a yearly seminar helping people who are scared to go outdoors at this time of year.
"The sound of the bells goes right to the unconscious," Hammerer told AFP. "We get people to confront their fears, we bring in people dressed up as Krampus."
Krampus performers say spectators can be the problem, grabbing their horns and throwing beer to wind them up.
Some groups held a demo in Klagenfurt recently to protest against negative media coverage.
But a whiff of danger is perhaps also part of the fun.
"There's a nice word for it -- 'angstlust'," the pleasure of fear, Wolf said. "People love rollercoasters for example. There's a kind of comforting frisson about it."
"When I was little I was a tiny bit scared," said Lukas, 13, getting ready in Schwadorf to appear in his Krampus disguise. "But then I became one."