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