Moncada, 19, hit .358 (57x159) with 29 runs scored, 16 doubles, 2 triples, 4 home runs, 30 RBI, 37 walks and 2 stolen bases in 54 games with the DSL Mariners in 2021. He led the Dominican Summer League in on-base percentage (.500) and OPS (1.060), while also ranking 3rd in slugging percentage, 4th in average (.358), T4th in doubles (16) and T5th in extra base hits.
Moncada was originally signed by the Mariners as a non-drafted free agent on July 2, 2018. He appeared in 39 games with the DSL Mariners during the 2019 season.