Here is the full list of all 36 Desperados III achievements.
Kill 31 hidden Mimimi devs.
Make guards follow Kate for 1,000 meters total.
Kill 200 guards using Cooper's double shot.
Kill 5 guards at once with dynamite.
Kill DeVitt.
Interrupt an important healing procedure.
Earn 90 badges.
Return the money to the bank.
Find a patient for the dentist.
Kill 10 small animals in one mission.
Jump from a tower into a cart of hay.
Knock out your father.
Kill all 3 golden chickens.
Kill 6 guards at once using only a single skill.
Execute a plan with all five characters.
Complete 5 of the Baron's Challenges.
Kill 75 guards with Bianca.
Hide 750 bodies.
In the first part of the mission, burn 5 guards at once with oil traps.
Enjoy some cupcakes during a picnic.
Snipe 50 guards with McCoy.
Decide the outcome of a duel.
Finish a mission on "Desperado" difficulty.
Mind control 25 guards with Isabelle.
Kill 1,000 guards.
Defeat Frank.
Kill 75 Long Coats.
Kill 15 of the hidden Mimimi devs.
Make someone follow your footprints for 25 meters.
Take care of DeVitt.
Meet Frank on a boat.
Kill 500 guards.
Hide 250 bodies.
Find Wayne.
Kill 50 guards using the environment.
Blow up a bridge.