$ perl -le'open $fh, "<:encoding(UTF-16le)", \"\xFF\xFE"; print length <$fh>'
1

$ perl -le'open $fh, "<:encoding(UTF-16)", \"\xFF\xFE"; print length <$fh>'
0

$ perl -le'open $fh, "<:encoding(UCS-2le)", \"\xFF\xFE"; print length <$fh>'
1

$ perl -le'open $fh, "<:encoding(UCS-2)", \"\xFF\xFE"; print length <$fh>'
UCS-2BE:Unicode character fffe is illegal at -e line 1.