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