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