subtype 'MyArray::Ents::Level2'
    => as 'ArrayRef[Str|Num|Int]';

coerce 'MyArray::Ents::Level2'
    => from 'Str|Num|Int'
       => via { [ $_ ] };

my $level2_constraint =
    Moose::Util::TypeConstraints::find_type_constraint(
        'MyArray::Ents::Level2');

subtype 'MyArray::Ents'
    => as 'ArrayRef[MyArray::Ents::Level2]';

coerce 'MyArray::Ents'
    => from 'ArrayRef[MyArray::Ents::Level2|Str|Num|Int]'
        => via { [ map $level2_constraint->coerce($_), @$_ ] };

...

isa => 'MyArray::Ents'