The previous year, a black half-tonne fighting bull gored his adopted younger brother Aryeh Deutsch, skewering his calf when he fell amid a crowd of runners racing just ahead of the beast in the San Fermin festival.
Despite the injuries Mulligan, a burly 43-year-old, and his brother, 40, are back in Pamplona this year to run with the bulls. This time, Mulligan has brought along his 18-year-old son Sam, who is taking part in the centuries-old fiesta for the first time.
Mulligan, from New Jersey, said he was nervous on Monday during his first "encierro" -- as bull runs are called in Spanish -- since being injured last year.
But he could not imagine missing the festival.
"It was good to get back on the horse," Mulligan said as he drank at a bar in a central Pamplona square that was packed with other runners dressed in traditional white clothes with red scarves around their necks.
- On crutches -
Mulligan spent a few days at a Pamplona hospital last July after he was knocked to the ground by another runner who was fleeing a bull that broke free from the pack during the fifth bull run of the nine-day festival.
After he returned to the United States, he had to use a wheelchair until the end of August and then got around on crutches or with the aid of a scooter until November.
"Everyone saw how much my injury affected me and they kept asking me if I would come back. Of course I would return," Mulligan said after he took part on Tuesday in the third bull run of this year's festival.
"It motivated me in my rehab. Anytime I felt like taking it easy and not do what the doctor said, I would make sure I got back on track to make sure I would not have any lasting effects so I could come back."
Mulligan and his brother have come to Pamplona to run with the bulls each year since 2004.
They have each taken part in more than 60 bull runs and plan to participate in all eight "encierros" of this year's festival.
"I run with the bulls in Pamplona, Spain, with my brother. The rest of the time I talk about running with the bulls in Pamplona with my brother," reads the description of himself which Mulligan has on his Twitter profile.
- Undeterred by goring -
The bull runs are the highlight of the annual festival, which attracts many international visitors and became world-famous with the publication of Ernest Hemingway's 1926 novel "The Sun Also Rises".
Each day at 8:00 am hundreds of people race with six huge bulls, charging along a winding, 848.6-metre (more than half a mile) course through narrow streets to the city's bull ring, where the animals face matadors and death in the afternoon.
Fifteen people have been killed since records started in 1911, most recently in 2009 when a 27-year-old Spanish man was gored in the neck, heart and lungs.
Deutsch, an engineer, said he does not let the memories of being gored stop him from running again.
"You definitely think about it but you don't let it get to you. You use it to your advantage and learn from it and keep on running," he said.
The two brothers prepare for the bull run through physical activities like jogging and have even visited ranches to observe bulls to get a sense of their instincts.
Sam Mulligan, who just finished high school, said: "I was nervous on my first run but I feel like I was better prepared than most others people because of my father."