SMITE

As Zhong Kui, use Expose Evil and Exorcism to fully stack your passive.

Zhong Kui's passive allows him to exorcise up to 20 demons, gaining two protections per demon. To capture a demon, use his first ability (Expose Evil) to mark minions or gods, then his second (Exorcism) to attack and absorb the marked enemies. A few waves of minions and this will come quickly.

Note that using his ultimate empties the demon bag, so you'll want to refrain from using it until you have the achievement.