This is a guide for anyone that wants to *start* on Zealot Difficulty. I do not recommend this move, however, as New Game+ makes life a lot easier. I did it play on Zealot first, though, so here's my advice to those bold enough to follow in my footsteps. I learned the hard way, so perhaps you can learn from my mistakes.
- Fully upgrade the Plasma Cutter! I had the Refurbished unlock from the first Dead Space, but the regular one will do. This will be the only weapon you are going to want to use for the majority of the game. It is quick to shoot, reload, and packs a punch on almost every enemy. Also, if it is the only weapon you carry, you will not find too much ammo for the other weapons.
- Before the first encounter with the Stalkers in Chapter 5, buy the Force Gun! These guys are the only enemies that gave me a hard time. They were too fast for the Plasma Cutter and ended me quickly. With the Force Gun, you can just put yourself in a corner or against a wall and wait for them to charge you. A single shot of Alt Fire will cause them to instantly die if you hit them head on.
- Run away, you may live to fight another day! I had a nasty habit of wanting to fully clear a room of all enemies if there were a lot of green crates around. I found that I wasted less ammo and health in the long run by running through a room and freezing enemies that got in my way. Sometimes it takes a while for the doors to open, so try to give yourself some breathing room and get out of there as fast as you can.
- Buy the Hacker Suit! On more than one occasion, only having to do 2 instead of 3 parts to the hacking mini game saved my butt and allowed me to quickly bypass some challenging and overwhelming battles. You may be tempted to buy other suits later on. I, for example, bought the Advanced Suit. This move hurt me really bad on money to spend on health and ammo during the final "gauntlet" before the end boss, so it is up to you if you think you have enough money towards the end of the game.
- For the part on top of the drill, run around like crazy! Enemies will be coming at you like a bat out of Hell. Bring lots of health and try not to stand in one place for too long. I barely made it through that part alive.
- Grab all of the semiconductors! You will need the money, believe me. In particular, if you find a diamond semiconductor, grab it! They're worth 25,000 credits. Some "mini-boss" enemies will drop them and there is one hidden behind a rock in the chapter where the giant drill is. You'll need all the creds you can get your hand on.
- You MUST buy and fully upgrade the Contact Beam before the final boss! The last store should be in chapter 13. Make sure you buy the Contact Beam; if you don't have enough nodes, respect the Plasma Cutter and fully upgrade the Contact Beam. I made the mistake of going to the final boss with only the Plasma Cutter and had to replay five chapters to get that weapon. The reason for its necessity is that one Alt Fire will cause the main target to show itself and it only takes 3-4 shots on that target to destroy it. It will make a difficult battle take less than 30 seconds.
- During the "final gauntlet" in chapters 14 and 15, run away! The Ubermorpth cannot be killed and there will be dozens of enemies. Run away, only stasis those that get in your way, get through doors to get checkpoints. You need to conserve as much ammo and health as possible for the final boss, so be quick and precise during this part.
- Make multiple saves! I saved a new slot every chapter in case I had to go back. This proved beneficial when I got to the final boss and had to go back. Would have been better if I had saved in chapter 13 instead of 12, but otherwise I wouldn't have been able to complete the game.
- Be patient! You're going to die a lot. Luckily there are checkpoints. If you can get into the next room, chances are you hit have hit a checkpoint. Stick with it, it will be a challenging 7 or so hours, but well worth the reward.
Good luck, hope this guide is helpful!