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