In this thread, I will begin with the original form of Emperor, Shin Getter Robo (from Getter Robo Go manga) and what it can do.
The robot that became the Getter Emperor by a process which I shall explain below:
Shin Getter Robo, aside from its normal weapons and abilities, is able to absorb just about anything via the use of the Getter Rays:
Energy (Vol7 Ch6)
Missiles (Vol7 Ch7)
Lifeforms (Humans, Dinosaurs, etc) (Vol7 Ch7)
Planets (Vol7 Ch7)
Now that we’ve gotten the process by which the Getter Emperor was made, as Musashi confirms, let’s move on to the Emperor itself:
The Getter Emperor is a gigantic robot (beyond solar system size according to a size video) made up of three ships like any other Getter machine, and is fueled by Getter Rays, the green energy source that propels the evolution of any life form (basically the original Spiral Power, color and all).
Brief Explanation of Getter Rays, from Getter Robo Armageddon:
Like I said, the original Spiral Power. They're also primarily green in coloration.
Emperor is ever-evolving, with no limits in sight to its growth in power and size. Musashi stated this in Getter Robo Arc:
As with Shin Getter Robo, Emperor also absorbs everything.
The 3 ships that combine to form the Getter Emperor:
Naturally, the fact that it has those 3 ships means that there are two other forms Emperor can take, like all Getter Robots, but we haven’t seen them yet.
Powers and Abilities
Getter Emperor wields an enormous amount of power, enough that it was able to destroy the universe after absorbing just one planet:
Followed up by the fact that just its combination alone was enough to quake the universe:
Its enemies say that it will devour the universe if left unchecked:
Getter Emperor can even crush sub-space:
While separated, it can wipe out entire fleets of ships and planets with just one Getter Beam:
Here's a video covering it in more detail than I may have here:
I hope you like it.