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