The Legendary Pokemon
Where are the legendary birds? (Kanto Region)
Articuno
Moltres
Zapdos
Where are the legendary dogs? (Johto Region)
Entei
Raikou
Suicune
What about the other legendary Pokemon like Mewtwo and Lugia?
All other legendary pokemon are considered bosses.
This includes: Mewtwo, Lugia, Ho-Oh, Kyogre, Groudon, and Rayquaza.