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