Ho-Oh

Ho-Oh is a -typePokémon introduced in Generation II. It is also known as the 'Rainbow Pokémon' and is often considered to be closely related to Lugia as a duo. Ho-Oh is also the trio master of the three Legendary beasts Raikou, Entei and Suicune.

How to Obtain
You can obtain Ho-Oh by doing the following:

Talk to the NPC in white at Saffron City's PokéCenter.

He will give you a riddle/list as follows:

"Mr. Weirdo. Opera. Tongue. Supercomputer"

Which means:

"Mr. Mime. Jynx. Lickitung. Metagross."

Have these four Pokémon and an empty slot in your Party and he will give you Ho-Oh. (Possibly Shiny or Aura)

If you don't get a shiny or aura just leave the game and rejoin until you get a shiny. You can also do this to any Pokémon who is given when interacted with an NPC (or himself in Necrozma's case).

Evolution
Ho-Oh does not evolve.

Recolors
The current recolors for Ho-Oh are shown below: