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