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