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