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