Gone are the days when playing with the yo-yo used to be a passing playground fad for teens.
Now the "fad" has evolved into a full-fledged performance sport, complete with a world championships, MTV-style thumping routines and yoyos that can easily cost upwards of S$200 a pop.
Credited for much changing the perception of yoyo-playing in Singapore, Marcus was the the world's No.1 player last year. He has his own sponsors, has two yoyos designed and sold under his name and even has his own YouTube channel.
One look at Koh's dazzling array of skills might inspire you to rummage through your storeroom to find your old Bumble bee yoyo and try the "rock the baby" or "walk the dog".
Having picked up the yoyo at the age of 10 after seeing children's animation "Super Yo-yo" on television, Marcus has helped redefine the art and has since gone on to be the world's best.
"It is more difficult now because there is a visual aspect to it," said Marcus of the game's evolution over the past decade.
"It's both a sport and at the same time, a form of performing arts because it provides entertainment to the people who watch it."
Even in international competitions such as the World Yo-yo Contest, Marcus said participants are judged on their routine, music use, style and showmanship apart from technical execution.
Watch Marcus' Kill Everybody-themed performance at last year's World Yo-yo Contest, where he was crowned champion for the 1A (single-hand) category.
Marcus is also one of the few Singaporeans who can claim to be the world's best at what they do after being crowned world champion at last year's World Yo-yo Contest held in Florida, United States.
He first participated in the world contest in 2008 when he was only 15. At the time, his father paid for everything because he had no sponsors then.
After finishing in 28th place and failing to qualify for the finals, Marcus promised himself to "practice everyday until I got better".
"I saw the ranking and felt really bad because I wasted so much of my dad's money to finance my participation in the contest," said the yoyo superstar of his first outing.
"Just the air tickets alone cost $3,000 per person," he added.
He went back the following year and except for 2010 when he didn't participate, his world ranking kept improving every year until 2011 when his big moment arrived.
"I cried like a baby when they announced I won last year. [I cried] because I've put a lot of effort, hard work and practice into it. It's like my girlfriend," Marcus said.
Marcus returned to the contest again this year to defend his title in Florida early August but was defeated by Japan's Hiroyuki Suzuki, who scored 83.51 against Marcus' 82.78.
He's a yoyo superstar
The only child in his family, his parents are extremely supportive of him. His mother, Mrs Adeline Koh, said yoyo-ing allows Marcus to channel his focus.
The usually shy, reserved teen -- who spend two to five hours every day to practice, and even more when competitions are near -- is completely transformed with his yoyo in hand.
Displaying a quiet, swaggering confidence during his routines, Marcus has made yoyo cool again through his MTV-styled videos which display his incredible array of tricks performed with alarming dexterity and speed.
He even has two yoyos manufactured under his name, one of which he helped design.
His first sponsor and yo-yo maker, Turning Point, gave him the Positron (MK edition) which retails for US$194.99 (S$244). But it was his, China-based Auldey, who worked with Marcus to design the Marcus Koh Signature ARES which retails at US$180 (S$225).
"I had the idea of my own yoyo for quite a while, it's just that I didn't have the resources nor the platform to engineer the yoyo out," he said.
"I worked with Auldey and drew out the profile of the yoyo. It has sharper edges and a longer mid-section, making it easier to do horizontal tricks with this yoyo," he added.
Marcus also boasts a global fanbase and even has his own YouTube channel that has racked over 100,000 views.
A quick search on Tumblr also shows many posts about Marcus and his yoyo tricks.
One time when he was competing in Russia, a female yoyo player kept grinning at him.
"I went over to introduce myself and she said, 'Are you the real Marcus Koh? Can I touch you?' and she just hugged me," said a beaming Marcus.
The next moment, she took out her tablet and said, "I have all your yoyo videos here".
So does it pay well?
Declining to reveal how much he makes, Marcus says he is earning enough pocket allowance to sustain his life as a teenager.
"At my level, in terms of skills and popularity, I don't think I can make a living from doing this professionally. I have to be better," he said.
World, you've been warned.