Sky Pillar's Deoxys .

In Pokemon Omega Ruby & Alpha Sapphire, after the player defeats the Elite Four for the first time, the player is able to complete the post-game quest: Delta Episode.

During the final act of the arc, the player rides Mega Rayquaza into space, with the aim to destroy a meteorite that is hurdling down towards Earth, threatening to decimate the Hoenn region.
With an unexpected twist, Deoxys emerges from the meteor, and will challenge the player to a battle, whilst being at the edge of space.
If the player failed to catch Deoxys, the player gets another chance at the summit of the Sky Pillar, after clearing the Hall of Fame again.

Regardless which encounter resulted in Deoxys capture, it's summary will indicate that it was caught atop Sky Pillar.

This marks the first time a Mythical Pokemon could be encountered in the core series games, without any special event requirements (ignoring glitching/hacks).

 

 

Species		Deoxys
Nickname		(default, save lang)
OT		(recipient)
TID		(recipient)
Distribution		In-Game Encounter
Location		Sky Pillar
Dates		(Various)
PID		Cannot Be Shiny
Games		ORAS

	Lv. 80

Nature		Random
Ability		Pressure
Item		None

Moves   (ITALIC means Relearnable)   Cosmic Power   Recover   Psycho Boost   Hyper Beam

Format Ver.1.0.6-2, Post Updated Date:20180430_1636