The Final Decision
The Final Decision is a difficult one, but you won’t have that much flexibility if you’ve maxed out your Karma meter, since you have to either fulfill your Karmic Destiny (if you are good, you have to choose Nix, if you are evil, you have to choose Kuo) or choose to quit and realign your Karma. To do this you’ll need to complete Side Quests or, and this is much faster, “grind” Karma by killing/draining or healing people.
Video: How to Adjust Your Karma
Good Karma Version (Choose Nix)
You MUST have at least a slightly positive Karma rating to make this decision to take on The Beast and fix the RFI. Head for the shoreline marked as a waypoint on your map. Use your Lightning Tether to latch on to the nearest boat.
Ride the boats across the sound until The Beast is in sight. When the boats turn around, start using the Lightning Tether to cross from boat to boat, heading south towards the shore and the waypoint.
Video Walkthrough of The Final Decision (Good Karma Version)
Once you hit land, head straight for the waypoint. It will lead you to a sub station on a rooftop in the Triangle. Pretty soon The Beast will show up. You’ll want to use your strongest powers on him, recharging frequently by nearing the substation. The quickest way to take out The Beast is by plastering him with Cluster Grenades, although Rockets work well too.
If he lifts you into the air, continue your assault. It doesn’t matter where you hit him. When half of his life is gone, Kuo will show up.
Kuo is easy to handle if you get her on the ground. To do this, toss Grenades at the base of her ice mounds and get them to crumble. When she hits the ground, nail her with more Grenades. This simple technique will knock her out of the fight in seconds.
Return to battling The Beast with your old techniques: Sticking grenades to its chest is a great, easy method.
Soon you’ll get the cue to summon an Ionic Storm. Press DOWN on the D-pad to end the fight. After the cutscene, head to the next waypoint in the church tower. Stand near the substation to initiate another cutscene.
You’ll have a new ultimate Bolt power now. As you float in front of The Beast, pummel it with Bolt shots to the chest. Soon its life bar will be depleted.
At this point Kuo will show up and you’ll have but one last action to take: Hold all four shoulder buttons to activate the RFI and end the game.
Bad Karma Version (Choose Kuo)
If you choose Kuo, you'll team up with The Beast for a city-destroying romp to the cathedral in the Red Light District.
Video Walkthrough of The Final Decision (Bad Karma Version)
Immediately run towards The Beast and jump up to tether to him. You'll essentially be able to fly alongside The Beast. Since there's no real goal for this portion of the mission, toss Bolts and Grenades at the people below for fun.
Eventually you'll come across Nix. The battle with Nix is prolonged thanks to her constant retreats. Perhaps the safest technique is to target her from afar with Precision Bolts, but you'll constantly need to drop to the street to Bio Leech bystanders for this energy-draining technique. Otherwise, just keep following Nix and trying to hit her with other attacks. Cluster Grenades work well.
After Nix runs off return to The Beast and jump up to tether to him again. If you get knocked off The Beast you can jump back up to re-tether to him. Once again there's no real object to this sequence, but you can fire at enemies for XP. In the plaza in front of the Can Can casino, Nix will stop you again. This time you should make sure you are above Nix, since she has a powerful beam that can keep you down if she maintains the high ground.
Either go right for her with close-range attacks or use Precision Bolts again. Once again, bystanders can provide you with power. She'll head back to the Can Can once you reduce her life to about a quarter.
Hit her with one more attack from the top of the tower and return to The Beast for another rampage.
The final battle with Nix is contained on one rooftop with ample spots to recharge. This means you can use close range, powerful attacks -- try stunning Nix with a Bolt and then sticking her with Grenades.
Run behind the tower on the rear of the church and charge up if you need a break.
The final showdown is with Zeke. After the cutscene, follow the button commands to bring Zeke to his inevitable demise. Since you've made your decision, there's no backing out now.