- Levin: Los Ticos regain grit in Ireland draw
Costa Rica completed their preparations with a hard-fought 1-1 draw with the Republic of Ireland in Philadelphia during the early hours of Saturday morning, despite having to play more than half the game with 10 men following defender Giancarlo Gonzalez's sending-off.
But 28-year-old Fulham striker Ruiz, who spent the second half of last season on loan at PSV Eindhoven, is confident they will be more than competitive as the four nations battle it out in Group D as they look to make it to the last 16.
Asked how Costa Rica's opponents would view the challenge they represent, he said: "They will think that it will not be easy to play against us.
"We showed in the second half that we can play with great character. They will know it won't be easy to beat us, but now they will know better."
Jorge Luis Pinto's men follow their opening fixture against the Uruguayans on June 14 in Fortaleza with a trip to Recife to face Italy on June 20, before ending their group campaign against England in Belo Horizonte four days later.
Ruiz is desperate to savour every moment of his time in Brazil, but is equally intent on ensuring that Costa Rica are not simply there to make up the numbers.
"It means so much for me to make it to the World Cup -- it's something I have been working for my whole life," he continued. "Now I have that chance and I am so happy. You never know when it will be your last.
"Of course playing against England will be special for me after my time in England, and I hope that it will be a match which will decide something, that one of us to go through to the next round.
"For us to get into round two will be a dream. That game against England could decide it."
If Costa Rica are to progress, they will need major contributions from talisman Ruiz and talented playmaker Joel Campbell, who Ruiz says is a "big weapon" for his side.
"I don't play against players, I play against countries. England, Italy and Uruguay are not about one player," said Campbell.
The 21-year-old was snapped up as a teenager by Arsenal in August 2011, but has been sent out on three season-long loan deals since, the last of them to Olympiakos, where he played Champions League football last season.
And Campbell added: "I only focus on my job. Last season I was at Olympiakos, so I was only thinking about Olympiakos; now after the World Cup, I will only be thinking about Arsenal.''
Assistant coach Paulo Wanchope -- who played in England for Derby, West Ham and Manchester City -- says his side can be fearless at the World Cup with no pressure to get results from a tough group.
"I was almost in shock when it was made," The Guardian reports him as saying. "I knew that it was going to be a difficult group but not that difficult.
"But we don't have anything to lose. The pressure is on the three others. I remember from my time in England just how much pressure there is on the England team."
Costa Rica's World Cup dream
Costa Rica head coach Jorge Luis Pinto discusses his team's World Cup preparations for a difficult Group D.
Men in Blazers: Can England advance from Group D?
The Men in Blazers look at Italy, Costa Rica, Uruguay and England to decide if their home country can advance out of group D.