my @ary = ( 1, 2, 3 );
for (@ary) {
    $_ = check($_);
}

# now flatten the list of mixed array refs and scalars into one list
my @tmp;
push @tmp, ref $_ ? @$_ : $_ for @ary;
@ary = @tmp;
print "$_\n" for @ary;

sub check {
    return $_[0] == 2 ? [ 'a', 'b', 'c' ] : $_[0];
}

__DATA__
1
a
b
c
3