Note: This is working on minions/jungle camps right now, so feel free to do it that way to make it even easier! Shoutout to commenters for confirming. I have left my description of how to do the achievement on gods below because there was a similar situation where a Tyr achievement that was supposed to be for hitting gods was working on minions, and Hi-Rez did patch it later (making the achievement harder).
The description of this achievement is: "As Cerberus consume the soul of every enemy god in the game with the use of his Soul Expulsion Ability."
When Cerberus hits an enemy with his third ability, Soul Expulsion, it creates a "soul" of their character (little ghost-looking things). Cerberus can kill these souls to "consume" them and heal. So essentially, you need to:
1.) Create a soul of every enemy god at some point in the game (by jumping on them)
2.) Make sure you consume the soul after doing that (easiest and quickest way to clear them out is by using your other abilities on a batch of them)
This is fairly straightforward and not particularly difficult. Do note that you can do it in the smaller modes since it doesn't specify five enemies, only "every enemy god in the game." I did it in a 3v3 Joust. So if you'd like to get it a little easier and quicker, smaller game modes for the win.