In late September 2018, Mozalev made his Junior Grand Prix debut in Ostrava, Czech Republic, where he won the gold medal.

He ranked second in the short program but won the free skate and outscored the silver medalist, Camden Pulkinen, by a margin of about five points.

[15] Mozalev debuted at the senior Russian test skates, including the quad flip jump, which he landed in the short program.

[17] With the COVID-19 pandemic continuing to affect international travel, the ISU opted to run the Grand Prix based primarily on geographic location.

Mozalev made his senior Grand Prix debut at the 2020 Rostelecom Cup, landing his quad flip in the short program but botching his jump combination, ending in sixth place in that segment.

[18] He was second in the free skate, despite doubling another planned quad flip, and rose to fourth place, less than two points behind bronze medalist Petr Gumennik.

[19] Competing at the 2021 Russian Championships, Mozalev took a "painful" fall on a downgraded quad flip to open his short program, placing fourth in that segment nonetheless.

[20] He landed the quad flip in the free skate, but a series of subsequent jump errors put him in fifth in that segment, remaining in fourth place overall.

[29] However, he was subsequently added to the European team following the withdrawal of Mikhail Kolyada, and won the short program with a new personal best, taking a gold small medal.

CS: Challenger Series; JGP: Junior Grand Prix Current ISU world best highlighted in bold and italic.