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