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