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