Not sure if it's possible to do what you want. An alternate way of solving it would be to have two block types, and one inherits the other.

Hi Todd,

When I've needed to do this I've generally taken the approach described by Erik but it should be possible to do what you're trying. If you create a validator like the following, implementing IMetadataAware then use it to check against a list of content types you pass in, you can set whether the field should be visible in the editor:

    public class HidePropertyValidationAttribute : ValidationAttribute, IMetadataAware
    {
        private string[] _restrictedPageTypes;

        public HidePropertyValidator(string[] restrictedTypes)
        {
            _restrictedPageTypes = restrictedTypes;
        }

        public void OnMetadataCreated(ModelMetadata metadata)
        {
            var contentMetadata = metadata as ContentDataMetadata;
            if (contentMetadata?.FindOwnerContent() is PageData pageData && _restrictedPageTypes.Any(x => x.Equals(pageData.PageTypeName)))
            {
                metadata.ShowForEdit = false;
            }
        }
    }

You can then use that validator on your property like this, passing in the names of the page types which shouldn't show the property:

        [HidePropertyValidation(new[] { "MyPageType", "AnotherPageType" })]
        public virtual string Description { get; set; }