Sandin began the year in the Swedish Hockey League and had a goal and an assist in five games with Rogle BK before leaving his home country to play full-time with Sault Ste. Marie. The Greyhounds lost the first matchup he played in but went on to win the next 23.
In 51 outings, he tallied 45 points (12 goals and 33 assists) before adding 13 more points (one goal and 12 assists) during Soo's trip to the OHL finals.
Sandin guarded the Greyhounds blue line with Avalanche prospect Conor Timmins in Sault Ste. Marie and was relied on while Timmins was out of the lineup, both with an injury and during the 2018 World Junior Championship.
"I think my coaches Drew Bannister and Joe Cirella who are both former defencemen have helped me a lot," Sandin told OHL.com about his time with the Greyhounds. "When you get to be able to play with Conor Timmins you learn a lot too. He is effective in any situation and he sees plays before they happen which is a special talent."
Sandin was the OHL Rookie of the Month for December with 9 points (two goals, seven assists) in 11 games and had an eight-game point streak while Timmins was at the World Juniors.
"Sandin is one of these unheralded prospects that came onto the scene and he was able to step right in and play an important role with Sault St. Marie," Dan Marr told OHL.com. "He's got very good vision, heads up game to advance the puck, make a real good pass in the zone, and at the offensive blue-line, he's got some composure and timing that makes him able to contribute offensively."
Sandin is the No. 11-ranked player on NHL Central Scouting's final list of North American skaters and the fourth defenseman on the list.