Not sure about mars lander without more info, screenshots or just the save would help.
As to cacodeamons, 2 of the imperial probes landed missions have them, also B rank wiz biz bounty has them too. Probably some others i can't recall, but those for sure
Well I got the Mars Lander/Zubrin (turns out I needed to capture a Belter - by the time I had completed those huge spaceship missions maybe they'd all died in the past? But this time I captured one and carried it back and aborted. Took ages because there are so many units on the ship taking their go during the computer's turn!)
I also needed a Study. The description hadn't made it seem like it did anything special, but it turns out the Robo Parrot I'd had for years and the Imp Corpse could ONLY be researched if I had a study, unlike 99% of the stuff in the game. Once I built one that research opened up (which is why I thought I'd done the Imp Corpse, because I'd taken loads back to my base in the past but not had any extra research options).
Here's my remaining issue: it looks like all I need is a Cacodemon corpse. However, in the 11 years of in-game time, I have never seen a Cacodemon (despite doing a number of Imperial Probes, Dark One terror missions, Doomed Farms etc). Since your comment above I have played another 18 months in game, taking days in real time, where all I do is shoot down enemy ships and do terror missions while waiting for Imperial Probes. In that time I have had five. Three were Deep One missions, two were Dark One. They had different names (one was Atrium, I can't remember the other). However, there was still no Cacodemon! Just the usual humanoid soldiers, Imps and Pinkies. As such, I'm wondering whether the version I'm playing has a bug that stops Cacodemons from appearing? After nearly one and a half years real time playing a single game, I assume one would have appeared by now if it could! So I don't feel like playing another week/two weeks/month if it turns out I can't find a Cacodemon.
Therefore, my request: is there a cheat to either create a Cacodemon, or or complete the Cacodemon research? If not, is there a cheat to get the research for the Conqueror ship so I can sidestep the Cacodemon and just build one? Many thanks!
PS I have also attached my latest save, from today (after just completing another Probe/Dark One mission; I also have saves from just before it, and maybe an autosave from during it).