answer:Mongooses is proper, but Mongeese is actually generally accepted. (in some circles at least). I personally believe that it should work in a numerical fashion e.g. Hemigoose, Mongoose, Digoose, Trigoose, Tetragoose, Pentagoose, Hexagoose, Heptagoose, Octogoose… all the way up to Kilagoose (1,000 Mongooses)