Any tips for the final battle?
I can't handle it
Which one is the "final"? The one with the generator horde, or before the A5 director's office? Anyway, those are somewhat related... The generator fight is pretty easy, but. Stack upon the lasers, the weight does not really matter too much as you don't have much space to run around anyway. Have a couple of brain smashers just should a boss run in when your turrets are dead. Place a laser on every platform, ignore the detectors etc. Some extra ones can be found in a room behind the control one, destroy the planks to get there. Seal every external door and window (ignore the one between the control room and a small entry one). Now just keep triggering the generators and keep an eye on the lasers (replacing them whenever necessary) in the control room and in the small corridor before it, do not walk outside! Alternatively, you can ignore the outdoor lasers and instead of killing the guys just shoot their legs off, this way they both won't neither make it in nor allow anyone else to spawn (though the monetary income is bad in this case).
The A5 one relates in terms of the laser usage, but is slightly different. Same preparations (though I also recommend buying some milk, which is the fastest healing option), but keep your stuff in the box this time, as you'll run, a lot! The first wave is trivial, but make sure to reach the container room on the second floor afterwards (applies to the other waves too). And DO. NOT. WASTE. YOUR. KNIVES! The second one may benefit from a couple of lasers if you want to, but I usually ignore them at this point. The third wave is the same as the second one, but everyone (but the runners ofc) has a blue gem, so lasers are a good option. Place anywhere you want, but be careful to not get stuck while running past a laser on the second floor! The third one is, guess what, the same again, but with red gems. Now, wage some war: mines, 'nades, second-floor lasers (the central arena is dangerous at this point), throw a smasher if things become grim... The safest way to hold on is to clear yourself some corner on the top floor and rifle away everyone from there, keeping your and some closer one lasers online (run away when needed, and do not get in a crossfire which is death). Next comes the boss fight which you can cheese with a single smasher, k, done.