upgrade to blast doors, this forces them to spend quite a bit of time trying to break down doors. so you vent the atmosphere and now they are stuck.
The boarders will notice that the atmosphere is gone, they will panic and STOP attacking the structure in the room and start pounding on the doors, they will manage to break 2 down before suffocating but as long as you make sure to move your people out of the way and keep on opening doors they WILL suffocate.
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It has happened to me a few times already that they ported into the oxygen room or a room adjacent to it. I currently play the Zoltan cruiser (loving that Zoltan shield and Halberd Beam) where you have to vent pretty much the entire ship to vent the oxygen room. And they seem to be quite focused (and rightly so!) on the oxygen generator. If they start attacking that, I have to stop venting, because I know I won't be able to repair it.
The invasion drone, now that there is scary.
I didn't meet those yet. I guess I'm in for a surprise.
Also annoyingly weapon "upgrades" are almost always massive downgrades.
Why is that? Most of the higher level weapons I have seen are rather focused on some specific strength of the lower level ones, but they seem to be really good at it. I like to have all 4 weapon slots filled, so I can really use their strengths correctly, preferably something like the Halberd Beam (for massive damage to lower level ships/ships with downed shields), some Ion weapon (to keep their key stuff disabled), Breach Missile (to get rid of their shield without giving a single damn) and some lower level faster charging missile (so I have something to use when my weapons array is damaged). The only problem of this combination is that it is completely useless against ships which have 3 bars of shields AND defense drone Mk2 (it will shot down the missiles and the beam is not powerful enough to get through the shields, even if the Ion weapon helps).
Loving it so far. The only issue I have is that unlocking the B type Kestrel is entirely luck based, whereas unlocking the b type mech cruiser is extremely easy. Oh well!
Most of the achievements feel luck base. Oh wait, the entire game is entirely luck based