Ghost Type
Perhaps is because the cannot target Normal types, and have an impression to attack themselves? Based on Pokemon Sheild, Allister described when he sends out G-Max Gengar, he mentions his loneliness
Dragon Type
Most Legendaries are dragon types, and based on the Hoopa movie, the Legendaries are always constantly fighting each other, also, based on the anime Fairy Tail, the protagonist had powers called Dragon Slayer Magic, which were used in ancient times in the anime to defeat other Dragons going berserk.
This makes no sense, I've hoped I've helped!