I Have Boa and it being 3 letters is rare plus has meanings (snake and I guess famous singer lol) but the rarest one I have is "Wasp" if I delete it, its lost forever so that's pretty rare I guess priceless as Its exclusive to me. Other blocked names like titanium or titan are simular. Rarest would be 3 letter original word names due to less word combinations available using only 3letters