Double the Fun! Achievement in Doom 3: BFG Edition
Double the Fun!10
Kill 2 Imps with one shotgun blast in DOOM 3, RoE, or Lost Mission
How to unlock Double the Fun!
The best way to get this one done would be to find two Imps and then save your game. Then get their health down using a weaker gun such as the pistol. Once both are weakened, try and get them together at an angle that would allow your pellet spread to hit both. If you miss, simply load and try again. The Super Shotgun might be better for this as it has a wider pellet spread.