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