Serious Sam 4

I believe level 1: Death from Above is the earliest you can get this achievement. Once you find 2 or 3 belchers in the same arena, clear all other enemies, leaving only the Belchers behind. Gently shoot all Belchers health down to about 25% with the Desert Eagle, drag them close together and pop/kill one of them. The collateral damage should blow the other Belcher up!