Enables mRNA (2'-O-methyladenosine-N6-)-methyltransferase activity. Involved in several processes, including forebrain radial glial cell differentiation; mRNA destabilization; and mRNA metabolic process. Located in nucleus. Part of RNA N6-methyladenosine methyltransferase complex. Orthologous to human METTL14 (methyltransferase 14, N6-adenosine-methyltransferase subunit). [provided by Alliance of Genome Resources, Apr 2022]