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