Here is the full list of all 36 Desperados III achievements.
Kill 500 guards.
Snipe 50 guards with McCoy.
Hide 250 bodies.
Kill 50 guards using the environment.
Blow up a bridge.
Kill 31 hidden Mimimi devs.
Earn 90 badges.
Kill 75 Long Coats.
Hide 750 bodies.
Kill 1,000 guards.
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.
Meet Frank on a boat.
Take care of DeVitt.
Defeat Frank.
Find Wayne.
Execute a plan with all five characters.
Kill DeVitt.
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.
Jump from a tower into a cart of hay.
Knock out your father.
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.
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.