Bulletstorm

Story related, can't be missed.

Act 4 Chapter 2

You'll get this after beating the boss, which is a giant plant monster. Just shoot it until it lets you shoot the red areas. It takes a lot of bullets, so buy ammo, charges, and the Flailgun to make it a lot easier.

Boss Fight

Info:
There are a few things you'll need to know before you head into the battle. There are a few phases to this fight, so I'll be laying them all out so you know what is next in each one and on how to deal with it. The Atrium where you fight, allows you to use unlimited slide, so use this to dodge the H-MF's attacks and get to better positions faster.

Around the outskirts of the Atrium are ammo boxes, so pick them up when you run low, though you can't actually run out of ammo during this fight! When you're sliding, make sure you don't get to close to H-MF as he does move around and also try and reload while sliding too!

Use the PMC and PMC only. If you have charged shots then feel free to give them a go. If you do swap to another weapon the Screamer is the next best weapon to use. Also the H-MF health bar is in red at the top of the screen. When the H-MF goes into regenerate mode and you start to shoot the red membranes/tentacles, if you look under it's health you'll see multiple blocks. These represent how many of the membranes/tentacles you need to kill. Once you've destroyed one, a bar will fade out from the bright red!

Phase 1:
Pretty simply start. The H-MF main attack is to use its branches out of the ground. Just keep sliding about and these shouldn't hit you, but watch out, one hit from these on Very Hard difficulty is a one-hit kill. The H-MF starts out on ground level and has multiple green/yellow spores around its belly area. Your objective to start is to shoot these out.

Concentrate on one until it bursts then move to the next one. When all are popped, the H-MF will thrash about then a sudden cyclone of pollen will burst throughout the Atrium. While this is happening you'll notice that on the H-MF some red membranes have popped up where the spores were. You'll need to destroy these, so either shoot or Leash them, but Leashing them is faster! When you see these membranes this is the H-MF's attempts to regenerate, so destroy them fast as once one is destroyed it can't grow back!

Keep sliding around the Atrium destroying these but if you miss one the H-MF will regenerate the spores and you'll have to destroy them all again to get the last membranes to pop back up.

Quick Phase 1 Kill - Do the above if you want to play fair, but there's a much quicker way to do this. Make sure you have loads of PMC charged shots and then when fighting the H-MF on the first phase, charge one up and shoot its neck/head. You'll take well over half its health off in one go, saving loads of time instead of sliding around shooting the spores.

Phase 2:
Once you've destroyed all the red membranes the H-MF will suspend itself from the roof of the Atrium and will now attack with its mouth. Keep sliding away so you don't get grabbed but if you do, spam the  until the bar reaches the top and you'll be set free.

Just keep shooting the H-MF in the mouth and around the body but watch out for when it drops a big bunch of spores. Try and maneuver between them so you don't get hit. Once you've dealt enough damage again, it'll drop from the roof and start to regenerate again. This time hit the red tentacle/worm like things that are in the same place as the red membranes. You can shoot or Leash these, again Leashing is faster. Again like Phase 1, if you don't manage to kill them all the H-MF will go back up to the roof for another round.

Phase 3:
Once all the red tentacles are down the H-MF will once again turn to the roof and start pumping blood to its heart. You'll notice its neck turn red and this is your new target. Just keep sliding from its lunge attacks and get in shots where and when you can.

You can also Leash the neck for some major damage but it is quite hard with it attacking you. Once its health reaches 0, you'll unlock the achievement.