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