Batman: Arkham Asylum

Achievement - Daydreamer
Survive the nightmare of the Scarecrow's fear gas

In order to get this achievement, you need to make it through a nightmare induced by the Scarecrow’s fear gas.
Once you’re in the nightmare where you find Gordon’s dead body, continue into the Morgue where you’ll see three body bags on the beds in the center of the room (Note – I actually had to exit the Morgue and re-enter it). After you open all three bags, the room will transfer into some crazy outdoor suspended location. In the center, the Scarecrow is spinning around a huge spotlight that you need to avoid. Basically, you’re running counter-clockwise around the Scarecrow in order to get to the Bat Signal.

Let Scarecrow spin around once or twice so you have a pretty good idea of the rate he spins at, then just get moving. Most of the fixtures you can just stand behind, but about halfway through, you’ll need to crouch (RT) against the bricks so you don’t stand over them.

About three quarters of the way around, you’re going to be standing behind a wall with three metal containers and to your right there’s going to be a wall. To get rid of this wall, you need to run over and spray it with explosive gel, run back to your previous spot and detonate it. When this explodes, Scarecrow is going to direct all his focus on the piece you are standing behind. Wait for him to look around the left of the fixture, then run and jump across the gap.

From my experience, he doesn’t leave that place for the rest of the time, so just move to the Bat Signal and get your achievement!

This is a good video showing how to beat the first scarecrow nightmare.

*This is not my video, all the credit goes to DrCJLong on YouTube*