He has won a total of 13 medals (six golds, five silver, and two bronze) at the Games of the Small States of Europe.

Mularoni made his official debut, as San Marino's only swimmer (aged 16), at the 1996 Summer Olympics in Atlanta.

[2] In 1999, Mularoni reached his breakthrough in swimming, when he earned two gold medals each in the 400 and 1500 m freestyle at the Games of the Small States of Europe (GSSE) in Vaduz, Liechtenstein.

Mularoni also proved his strength in long-distance swimming at the 2000 Summer Olympics in Sydney, when he decided to compete in the 1500 m freestyle, which was later dominated by host nation Australia's Grant Hackett.

[5][6] He qualified only for the men's 200 m freestyle by clearing a FINA B-standard entry time of 1:53.87 from GSSE in Valletta, Malta.