Geist/Bosses

Creature (Hydra)
Strafe back and forth and shoot at its mouth when it is wide open. Whenever it's not screaming at you it will either be protecting itself or it will be shooting orbs of energy at you. Dodge them, keep strafing, and keep shooting its mouth. After 15 shots it will retreat into the ceiling, ending the fight and enabling you to pass. Even if you do die, you just reached a check point so don't worry. The damage from the orbs are minimal, but don't go anywhere close to its claws or it will take your health down in just a few swipes. You can't slip by underneath, you'll have to duke it out to the end. An easy way to fight it is to put your crosshairs on its mouth, make sure you can hit it, then just strafe back and forth without ever adusting your aim. Even though you'll be strafing, you will automatically turn slightly to be always facing it; just pull the trigger when need be.

Attacks
He just ate your friend, whom you spent so much effort to revive, so hopefully you're pissed. This guy is immune to all shots while he's protecting his head, and he'll fire a single blue orb every once in a while. If you get too close, he'll try and swipe at you a few times. If you've damaged him a little, periodically he'll begin to fire large amounts of blue orbs at you in the form of random horizontal spreads. These spreads come in three, four and five orb groupings; it's best to try and dodge in between them. He'll fire around 14 groups before stopping. After getting him down to around 50% health, he will release a golden beam of energy at you. As you strafe away, he'll continue to follow you with it so just shoot him while you have the chance. His final attack comes in a devastating rolling charge. The beast will retreat into his shell, dislodge itself from the center and then roll around the outside ring trying to hit you. It will alter it's path slightly on each revolution, switching from either the side closest to the inner ring, or the side closest to the outside wall. When it starts getting close to you, just run to the other side (if you're against the wall, run towards the center of the room and visa versa). From this point on, he will begin firing three orb groupings at you instead of singles while he guards himself. When you get him to about 10% health left, he'll dislodge himself from the center one last time. However, he'll be glowing blue. As he charges around, fire at him and he'll come to a stop. Run around him and lob a grenade in. Do it twice and his shell will explode and the beast will retreat.

How to Damage
Run up to him, have him lower his guard and swipe at you but back up before he can hit you. Fire at his face while his arms are busy. After taking some damage, he'll retreat into his shell; lob a grenade in to deal some massive damage.

Boss (Hydra, second one)
Like Creature.

First Helicopter
There are two ways to approach this boss, the easy way and the hard way. The easy way will make the fight only a few seconds long and will guarentee victory, but the advanced one will benefit you after defeating it.

Easy method
Immediately dispossess from Raimi and float across the Helipad. Possess the anti-aircraft missile launcher and take down the helicopter with three shots. Be careful, you only have six missiles!