Capefeather
While Birkal's idea is intriguing, it seems too similar to a number of already-existent Pokemon, including Gastrodon, Ferrothorn, Skarmory and Blissey. These Pokemon completely counter certain Pokemon, or have perfect counters themselves. For example, Gastrodon is a perfect nemesis for Politoed, but has a perfect nemesis in Ferrothorn. Ferrothorn is a perfect nemesis for Starmie, but has a perfect nemesis in Heatran. Thus, I fail to see what we could learn by doing this.