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