How to repair the O2 Generator in an oxygen deprived ship

When boarding, I tend to aim for the Oxygen subsystem room - it's typically small, and critical enough that I will quickly attract attention. If they don't respond, then I've pretty much sealed their death quickly.

Meanwhile, I'll target whatever critical system I choose (usually weapons, shields, drones, or engines) with my laser weaponry. Once I've hurt one or more of their crewmembers, I'll target the medbay with missiles or bombs. That way, I can finish off heavily wounded crewmembers while disabling their ability to heal. Fire bombs and subsystem bombs are the best for this sort of attack.

I do believe that firing on the rooms where your boarders are will hurt them as well as the enemy, so I tend to avoid this. Trying to get the timing right for lasers (to reduce shields) + beams (to do damage) is also kind of tricky if you're also monitoring a boarding party.

Also, it helps if you've got a couple of teams of boarders - while you're healing the first squad, send the second squad in to keep the pressure up.

Some ships are particularly bad for trying to board, however. If they've got significant crew, especially a lot of mantises, I may give up trying to win by wiping them out. On the other hand, getting into an engagement and realizing they have no medbay pretty much means I've got a win locked down.

As you've noticed, Rock and Mantis crewmembers are the best to send as boarders. Don't forget that you can pause the game with the space bar, so if you think getting your crew back on board is going to be a close call, pausing and unpausing to slow the game down may help you slice the timing razor-thin.

Possible spoilers if you've never been to sector 8:

It's also been noted in a couple of strategies for fighting the final boss that the weapon systems are in isolated rooms with just a single human guarding each. If you send 2 of almost any race of boarders into these rooms, you can kill the guard and disable the system, thereby making this fight easier. The best weapon to start with is (in my opinion) the missile launcher, which is third from the left.

Having had to depend on an Ion/Beam combo, I've worked out the Critical thing for Ion Weapons is consistency.

As agent86's answer says, Multiple hits within the "Lockdown" period stack, but the minute that timer runs out, the locked system restores to full.

So your aim is to keep the lockdown timer on any disabled system from running out. Therefore you should be focused on ensuring on repeatedly hitting one system within its period rather than spreading ions around other systems.

To illustrate; if you bring shields down to 0 with ion, then target weapons, you have to hit the shields again before the lockdown on the shields lifts, otherwise they'll restore, and then while you're bringing them down again, the lockdown you've put on the weapons will lift.

If instead you keep hitting the shields, you'll keep resetting the lockdown timer on them and they'll stay down. At this point your other weapons pick up the slack and tear into the non-ionned systems.

Once you have low enough shields that other weapons can penetrate (e.g. your lasers can bring them down, or your halberd/glaive can breach them), you want to focus at least some of your system damage on the helm and engines. Remember, every miss with an ion weapon is bringing you closer to a timer reset.

One useful trick is to alternate between ionning a single system and the shields (e.g. one to the shields to reset their timer, then one to the weapons to lock them down). However you increase the chance that one miss will lead to the shield lockdown running out, especially with the slower Heavy Ion cannons. (Which is why faster ion blasters are more expensive/require more power than ones that do more damage).

Other useful tips:

• Even after a lockdown lifts, weapons and shields still need to recharge their buffers.
• Lockdown damage and real damage doesn't stack.
• The Cloak time is longer than the Ion Timer, so cloaking is a great defence against Ions. How much of a problem this is depends on your Ion capacity and the enemy shields, but you need to disable it. Got into a complete stalemate with the boss based on this...

I hope this helps!