The comment section has spoken and the final victor is... Krieg!
Before I start here's what I would have written if you guys had chosen the Forge world or Macragge.
A forge world would have been interesting with all the skitarii and all their cool toys like Rad guns, Vortex guns, Disintegration guns, Conversion Beamers or Grav guns.
I can even give them Primaris Space Marines as the Forge world I was planning to send there is Mars if you guys picked Mars. There might even be some Dark age super weapons like the nano-phage that is heavily implied that mars poses in the Beast Arises book series.
In that same book series there was a plot by the fabricator general of teleporting Mars away when the beast came to Holy Terra which I was going to use if you guys had chosen the Tech-priest.
As for Macragge? they would have along with the Ultramarines, a Primarch as Guilliman would have been revived. I have mixed feelings about that filthy Xeno armour that revived him, despite the fact that there has been hints through out the series that his wounds have been slowly healing in the stasis. I feel that GW could have written it better.
Then again I'm just an amateur writer trying to lecture real writers especially with my clearly top tier Shakespearean English.
So without further ado story start!
Oh and if any of you writer want to use my ideas your free to do so.
—- story start—-
On a desolate planet deep beneath the radiated surface of the planet Krieg a Magos was just experimenting on a teleportatium, he was trying to make the teleportarium teleport bigger things.
You see this is why you don't try to innovate, unless you roll a critical on your dice rolls you're going to fail miserably, especially when you're dealing with technology based of ork technology.
You see somehow this little magos managed to dig up an old file pertaining to some old records during the 32nd millennium about some super teleporter.
Suffice to say something has gone wrong because as soon as he started the device. A bright flash suddenly overloaded his sensors followed by a moment of weightlessness before he landed back on the ground, next he could feel a slight tremor on the ground as his mechanical eyes have rebooting.
Not long after his sensors are suddenly picking up a sudden surged of Vox communications.
He intercepted a few of them to analyzed their content to see what's the sudden commotion is all about.
"report! The celestial bodies has changed!"
"report! the Astronomicon has disappeared!"
"report! All in bound shipments has gone silent!"
"report! We've lost all communications with all near by Imperial forces!"
A series of reports from station commanders and ship captains flooded the Vox chatter.
Upon further investigation he arrived at the conclusion that the sudden surged of Vox communication is due to the entire planet being teleported.
The Magos frozen for a second as it seems that the realization has overloaded his circuits for a bit. It didn't take long before he has booted his system back up again and rechecked his systems for any logic errors.
He checked and rechecked but everything is running at optimum conditions.
The Magos stood still as he just arrived at the conclusion that he just teleported the entire planet of Krieg to... To by his calculations another galaxy.
The Magos frowns as his robotic eyes narrowed.
'this should be impossible' he thought as there's simply now way with the amount of power he has put into the device and the device he has constructed shouldn't be able to contain the powers needed to teleport a planet.
He then checked the logs to see what exactly happened that might has caused such an out come.
Not long after he found that as he was conducting the experiment there was a sudden warp spiked coming from the cadian sector. The seer scale of the spikes is the largest ever in recorded imperial history.
Upon further analysis he concluded that it's probably due to the this sudden spike of psychic warp energy that supercharged his device that sent him and the entire planet of Krieg millions upon millions of light years away.
He doesn't know what major event is happening at cadia right now but judging by the sheer scale of the spike in warp energy it's really big.
As he's thinking about that he suddenly received a vox communication form the planetary governor.
A few moments later after when he arrived at the planetary govenor's office, the planetary governor wasted no time in telling him that he knews that he is the one responsible for this disaster.
The planetary governor sad that gently with a normal tone of voice but the magos knows that the planetary govenor is... Not in the best of mood shall we say and one wrong word could lead him to being recycled for scraps.
Fortunately his logic engines seems to be working at top condition as it took only a fraction of a second for him to come up with a suitable reply to they himself out of this mess, while he does admit that he is "partly" responsible.
He explains that something has happened in the cadian sector that cause a sudden spike in warp energy which interfered with experiment, saying that he also mentioned to the governor that he is the best chance of sending Krieg back.
Hearing said that the planetary governor's brows quirk and asked "Can you reverse it?"
"reverse it?..." the magos then goes on a bit of the details and tells him that its... possible but it'll take some time.
Truth be told the magos highly doubts that he could recreate it much less reverse it but it's not really a lot when he told the governor that it's reversible but it's just very very very very very very unlikely.
A few moments later after a bit more dissociation the magos somehow manages to exited the room in one piece.
The magos gets to live another day.