The quartet will be the star attractions for the many hovering scouts in India when England, attempting to reach the final for the first time, take on Brazil, and Spain play Mali.
Mali striker N'Diaye, the tournament's joint leading scorer with five goals, could be the prize catch.
A product of the street game in his home country, N'Diaye was only drafted into the national squad ahead of the qualifying tournament in August.
Coach Jonas Komla spotted the teenager at a league match and told him to join the national team.
"The first time I went, he told me I was too small. I was really angry, but I knew that could happen because nothing is easy in football," N'Diaye told FIFA.com. "A few months later, he called me back to say that, in the end, I could come along and train with them as I'd grown a little. I was very happy. And now I feel comfortable in this team. I feel that I have responsibilities, and my teammates have faith in me to score goals."
Mali are the African champions, while European title-holders Spain will be counting on centre forward and captain Ruiz to show his class.
The Barcelona academy product already has four goals in the tournament — including one in the quarter-final win over Iran — and has been linked to Arsenal and other Premier League sides, as well as Juventus.
Ruiz already has a buyout clause of only €3 million on his contract and Barcelona reportedly want to increase that after the World Cup is over.
Brazil are normally known for producing goalscorers, but their campaign for a fourth U17 world title has relied heavily on goalkeeper Brazao and his spectacular saves in India. He has not let in a goal from open play at the tournament.
The Cruzeiro stopper has been hailed by Brazil U17 coach Carlos Amadeu as well as opposition tacticians like Spain's Santiago Denia, who said Brazao could play at the "top professional clubs in the world".
Brewster, who scored a hat-trick in the 4-1 quarter-final win over the United States, is another pressing for first-team action, in this case at Liverpool.
The young attacker has been the focus of England's bid since Borussia Dortmund called back teen star Jadon Sancho after the group stages.
Brewster made it to the substitutes' bench for Liverpool in April and coach Jurgen Klopp has hailed him as "wonderfully skilled".
By putting a goal past Brazao, Brewster would send the perfect message to Klopp. But he is not counting on anything.
"You don't really get many opportunities to play at the international level and you have to make the most of it. And it will be the same at the club level too. I have to make the most of my chances," he said.
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