Got it from killing Knights
Here's how I got it:
I read in another forumthread that someone got i from killing Knights(those big flying things with the tail) and that they replayed the WHOLE 1-5 Village Attack just to get 3 Knight-kills.
The first time you encounter a Knight in "Village attack" you get a checkpoint just before, so I figured "shouldn't you be able to kill it with a grenade, kill yourself and repeat?", so I started doing that but got insecure after 6-7 kills and started doing the method mentioned in this thread with the blowing the door-thing. It didn't work for me so I went back to killing Knights by rinsing and repeating at "Village Attack". 2 kills later it popped! That proves that rinsing and repeating works and doesn't need a checkpoint or anything to save the kills since I killed 7 and 1 more for the "Big Bang"-achievement. 2+1+7=10! HA!
So, here's my method:
(AND JUST TO CLEARIFY, IT'S ON XBOX360 I PERFORMED THIS, NOT PS3)
1.Start up 1-5 "Village Attack" on Casual and make sure you select the "Disintegrator" as one of you weapons.
2. Kill the puny 3 droids with melee(it's quicker) and continue over the bridge.
3. After the cutscene a Knight will rise from the abyss(....yeah, man!).
4. Shoot it with the Disintegrator until it does a recoil move, that means it's hurt.
5. Shoot it TWICE, and only twice more with the Disintegrator and it will start bleeding blue gas.
6. Cook the grenade and throw it close to him, making him explode in glorious... exlosioning(...?)
7. Take a deep breath and take a leap of faith into the abyss from hence the Knight came from, killing you.
8. You will start right back up right in front of the rising Knight.
9. Repeat until it's 10 times and I hope you get the achievement.