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