@vinnyIMPORTANT before committing to special stuff, that big UFO (the Overseer) is NOT the end mission. The game will make it very clear when you approach the final mission. And you absolutely need the psy-lab and a psionic soldier for completing the game.
Also, Dan has already estabilished that he's not really into it anymore in the last 3 of his turns (he goes in, finish the first mission that pops up the fastest way he can and bye) so he's not into the strategic layer anymore and it's useless to leave it to him to build stuff. Abby is doing a good job on the missions side but has no idea of what to do as base management (because she never played before and the structure of the feature). It's really up to Alex to start doing that stuff.
You'll need at the bare minimum two new structures to finish the game (the aforementioned Psy-lab and a later story one), so by now doing this is only prolonging the game. You'll need days to excavate the rooms, others to build the necessary structures, then more again to find a soldier who is a psionic.
If you want to build anything else (like for example a satellite nexus to have enough capacity to cover the remaining countries, for which btw you could already start to build the satellites) you will also be in need of more power, so a thermogenerator on that steam should be enough to cover any desired new chamber. Right now you guys are not really moving toward the end, which is not right around the corner like you seem to think; you could already start shortening the time needed by at least excavating a few blocks and starting the process of testing as soon as you build the psy-lab
@blacklagoon: you are totally right, which is frankly insane that they didn't even correct it in a patch since it's quite glaring. Oh well then, better this way then i guess?
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