OK, let's give this one a try:

Outlaw and A Boy and His Blob - both programmed by David Crane.

Turrican II and Dynamite Deka - Both games are related to action movies:  Turrican II became Universal Soldier while Dynamite Deka was made after licensing from Die Hard.

Xybots and ElectroCop - both published by Atari (seems rather obvious but I can only find limited info).

Checkered Flag and Rogue Trooper - both made by Rebellion.

Soul Star and Ninja Gaiden - neither game saw release.

OK, let's give this one a try:

Outlaw and A Boy and His Blob - both programmed by David Crane.

Turrican II and Dynamite Deka - Both games are related to action movies:  Turrican II became Universal Soldier while Dynamite Deka was made after licensing from Die Hard.

Xybots and ElectroCop - both published by Atari (seems rather obvious but I can only find limited info).

Checkered Flag and Rogue Trooper - both made by Rebellion.

Soul Star and Ninja Gaiden - neither game saw release.

Well done! 4 out of 5 right!

Electrocop was by Epyx  😉

Well done! 4 out of 5 right!

Electrocop was by Epyx  😉

Ah, that's why I was specific about published.  LOL  Atari published them both.  Epyx programmed Eletrocop and Atari programmed Xybots.    I'll see if I can find more.

Different Atari though as Xybots was Atari Games/Tengen 

Give up?

I can't find the last answer.  Maybe someone else gets it. 

Nobody has got it so I will give you the answer:

They were both originally supposed to be the third game in a popular series!

Xybots was Gauntlet 3 and Electrocop started life as Impossible Mission 3

Nobody has got it so I will give you the answer:

They were both originally supposed to be the third game in a popular series!

Xybots was Gauntlet 3 and Electrocop started life as Impossible Mission 3

Xybots was Gauntlet 3?!  Wow, never saw that one coming.  I had heard about Electrocop starting as IM3, though. 

Yes it was originally supposed to be a 3D Gauntlet game but when Atari felt the game was getting too far away from its roots they had the graphics changed to a space theme and renamed it.

Yes it was originally supposed to be a 3D Gauntlet game but when Atari felt the game was getting too far away from its roots they had the graphics changed to a space theme and renamed it.

Cool!  Where do you find this stuff?!? 

Yes it was originally supposed to be a 3D Gauntlet game but when Atari felt the game was getting too far away from its roots they had the graphics changed to a space theme and renamed it.

Cool!  Where do you find this stuff?!?

I read it in an interview with Ed Logg, the coder.

Now that's some obscure trivia! Cool to know that's how Xybots got it's start.

Yes it was originally supposed to be a 3D Gauntlet game but when Atari felt the game was getting too far away from its roots they had the graphics changed to a space theme and renamed it.

Cool!  Where do you find this stuff?!?

I read it in an interview with Ed Logg, the coder.

Very cool!

Ok then here we go with 5 new retro relations!

Knightlore - Spectrum                                    WWF Wrestlemania - NES

Pengo - Mega Drive                                                          Gale Racer - Saturn

Commodore Pet                                                            Atari Jaguar CD

Target Renegade - Spectrum                                          Human Killing Machine - Atari ST

Scrapyard Dog - Lynx                                                  Basketbrawl - Lynx

Gale Racer was a Japan only release for Sega Saturn, converted from Rad Mobile coin-op (and really should have seen a MCD conversion, rather than appear on Saturn).

MD Pengo was Japan Only release.

Human Killing machine was touted as a home computer sequel to Street Fighter and Target renegade was for Renegade.

Scrapyard  Dog+ Basketbrawl, both (converted from?)/avaiable on Atari 7800.

Was'nt a Speccy owner,nor Jag CD owner, never touched a PET computer, loathe wrestling so stumped on those.