Just Cause 4

A whole Army of Chaos achievement will be awarded along with Rico's Roughnecks achievement, both achievements are unlocked when you reach chaos level 14.
This method took me 45 min to reach level 14 from level 10. Each level after level 10 requires a minimum of 2 million chaos score. This is probably the fastest method I found.

Full credit goes to FDKsyn on Youtube

I recommend destroying as much enemy vehicles and destructibles as you can during your playthrough so you don't have to grind this.

Unlike Just Cause 3, you don't actually need another person who also owns the game in order to get this achievement. There are multiple records shown in the Feats menu that are set by the developers. Simply track one of them and beat it to unlock this.