Mari has joined the Gunners from Flamengo on loan for the rest of the season.
He had previously been with Manchester City before moving to Brazil, but made zero first-team appearances for the Sky Blues.
Speaking to Arsenal's website, Mari said: "It's a massive opportunity for me to come to England, which is the best league in the world right now.
"Being able to play in this league and having the opportunity to play for Arsenal is incredible, so I'm really looking forward to wearing the shirt as soon as possible. I want to help my team to win matches and give my fans something to celebrate.
He added: "I want to take it one day at a time and achieve big things at Arsenal.
"Right now I want to focus on the day-to-day side of things. I think we need to put the plans to one side for now because the most important thing is to take things one day at a time and focus on achieving short-term goals.
"We need to change the dynamic around the team, so the short-term objectives are the most important thing. As I've said, we have Mikel's ideas, aligned with the club, and we need to perform very well to change things."