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