Here is the full list of all 36 Desperados III achievements.
Kill 75 guards with Bianca.
Hide 750 bodies.
Kill 75 Long Coats.
Kill 1,000 guards.
Defeat Frank.
Mind control 25 guards with Isabelle.
Make someone follow your footprints for 25 meters.
Take care of DeVitt.
Kill DeVitt.
Jump from a tower into a cart of hay.
Kill 5 guards at once with dynamite.
Kill 50 guards using the environment.
Meet Frank on a boat.
Kill 500 guards.
Find Wayne.
Hide 250 bodies.
Blow up a bridge.
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.
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.
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.
Kill 15 of the hidden Mimimi devs.