Geist/Bosses

Hydra
Strafe back and forth and shoot at its mouth when it is wide open. When you've taken about a quarter of its health, it will start shooting orbs of energy at you. Dodge them, keep strafing, and keep shooting its mouth. Eventually it will go into the ceiling, and you can pass.

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.

Hydra (second one)
Like Creature.