The Necromorphs in Dead Space come in a wide variety of forms. Here are the monsters you'll face in order of appearance.
1. First up is the Slasher, the most common Dead Space foe. Their scythe-like appendages and powerful jaws mean that the Slasher should be defeated before getting too close. You'll encounter your first Slasher early in Chapter 1.
2. Perhaps the most twisted creation of the Dead Space development team, Lurkers are the reanimated corpses of cloned babies harvested aboard the Ishimura for spare parts. The three tentacles of the wall-climbing Lurker can launch projectiles which cause moderate damage. If the Lurker gets too close you'll take increased damage from the more-powerful melee attack. Trim the tentacles quickly when they first flare out for a quick kill. First encountered in Chapter 2.
3. The scorpion-like Leaper's tail is spiked with a deadly stinger. Defeat the melee-only Leaper from a distance before he closes in with his powerful leaping ability. First seen shortly after your Lurker encounter in Chapter 2.
4. Swarms are the creepy-crawlies of Dead Space. Individually not much of a threat, their large numbers make them a deadly annoyance. Stasis them to concentrate the firepower of your Force Gun or Line Gun Mine. First seen in Chapter 2.
5. Infectors are the force multipliers of Dead Space. Their tough hide, lack of severable appendages and ability to reanimate corpses require rapid fire and a bit of planning; dismember any corpses in the area when Infectors are about. First seen in Chapter 2.
6. Most Necromorphs also appear in a Super variety. These barbecued Necromorphs are faster, tougher and more deadly than their normal counterparts. Tactical retreat, Stasis, and a well-upgraded weapon are your best countermeasures. First seen in Chapter 2.
7. Drag Tentacles pull you through their tunnels to a certain death unless their vulnerable yellow nodes are destroyed. Rapid fire with the Plasma Cutter has always been my preferred solution to their sudden attacks. First seen in Chapter 3.
8. Pregnants are a fatter, lumbering version of the Slasher. Be sure to avoid shooting their belly which will birth a Swarm if pierced. First seen in Chapter 3.
9. The first time you encounter the Brute in Chapter 4 is the toughest he'll be all game. This boss variety is much harder to bring down than the regular variety you'll encounter later. His vulnerable red and yellow areas, mostly on his back, are the place to aim while shooting. His tough melee attack is supplemented by an ability to toss yellow projectiles which, when caught with Kinesis, will earn you the Playing Catch achievement once tossed back. The Brute is one of the few Necromorphs that are well-suited to a Flamethrower attack.
10. Another Flamethrower-friendly foe are these Divider segments, first seen late in Chapter 4. They aren't finally seen in their fully-assembled form until Chapter 8. Similar to Swarms, individual segments aren't much of a threat, but their quick speed and large numbers can make them a deadly annoyance. Stasis and rapid Plasma Cutter fire are my preferred solution.
11. Guardians are immobile, wall-mounted Goliaths that protect important doorways. First seen in Chapter 5, Guardians are easiest defeated by tossing an explosive canister with Kinesis. Later in the game when no canisters are available you'll want to use a Cutter Blade or Line Gun Mine. Kill them quickly before they can launch projectile-shooting Pods. Guardians don't die until all of their sprouting tentacles are severed.
12. Dr. Mercer's ultimate creation, the Hunter, is arguably your toughest Dead Space foe. The Hunter's relentless pursuit is made possible by an ability to regenerate severed limbs, making him unbeatable by conventional means. Hobble him by shooting his legs or use Stasis to slow him down when you first see him in Chapter 5. He can initially be defeated by freezing in the cryo-chamber and then ultimately destroyed by incinerating him with shuttle engine fire.
13. Wheezers pose no immediate threat other than the toxic fumes given off by their mutated lungs. The only time you'll encounter this Necromorph type is in Chapter 6.
14. No Necromorph can match the creepiness of the Exploder's strange vocalizations. When you first hear their almost-human voices in Chapter 6 you'll know something wicked this way comes. Their explosive sacks are both their primary weapon and their greatest vulnerability; shoot the sack and destroy the Exploder in the subsequent explosion.
15. The Leviathan caps off Chapter 6 and is perhaps the longest boss battle in Dead Space. Pop the vulnerable yellow nodes with your Plasma Cutter then grab his yellow projectiles with Kinesis and throw them back into his mouth. Doing so will earn you the Playing Catch achievement if you haven't already earned it by doing the same with the Brute.
16. Pods are first seen without their Guardian counterparts in Chapter 7. These immobile, projectile-throwing oddities can be easily destroyed by severing their single appendage.
17. The lanky Divider is deceptive in form and function. The seemingly-slow Divider splits into speedy segments when fired upon, resulting in a Swarm-like mass of smaller targets. Stasis, then fire in quick succession to eliminate the grouping quickly. First seen fully-assembled in Chapter 8.
18. The Slug is a Chapter 8 boss battle reminiscent of the asteroid segment in Chapter 4. Use the Ishimura's Mass Driver to pop the Slug's vulnerable yellow nodes. He'll then separate from the ship and drift into space.
19. Twitchers are the reanimated corpses of Marines stationed aboard the USM Valor seen in Chapter 9. These Slasher-like foes are wickedly fast but succumb to weapons fire rather quickly. Act fast and they shouldn't cause much trouble.
20. Seen in Chapters 11 and 12, Tentacles are similar to Drag Tentacles and the tentacles seen on the Leviathan and Slug. This variety will try to slap you then swipe the ground hoping to knock you over. As always, the vulnerable yellow node is your target.
21. The Hive Mind is Dead Space's final boss. This collective consciousness controls the actions of all Necromorphs. Defeat the tentacles by targeting the vulnerable yellow nodes while strafing left and right to avoid being knocked down. Destroy the yellow nodes inside the Hive Mind's chest to defeat him and win the game.