using Flurl;
using Flurl.Http;
using Nullforce.Api.UrlBuilder.Derpibooru;
using Nullforce.Api.JsonModels.Philomena;

...

var derpiClient = new DerpiClient();

// The Derpibooru API expects a user agent string, use yours here
FlurlHttp.ConfigureClient("https://derpibooru.org/api/v1/json", cli => cli
    .WithHeaders(new
    {
        Accept = "application/json",
        User_Agent = "your_user_agent_string"
    }));


var searchResult = await derpiClient
    .Search()
    .WithQuery("fluttershy")
    .Page(1)
    .PerPage(50)
    .Uri
    .GetJsonAsync<ImageSearchRootJson>();

foreach (var image in searchResult.Search)
{
    Console.WriteLine($"Downloading {image.Id}...");
    var path = await image.ImageUri
        .DownloadFileAsync(@"c:\downloads");
}