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