You can complete this solo,
This is how to defeat Puerta Del Eden Special Operations on Mastery 3 solo.
The equipment I used is
Gladiador Supremo
with Poison Proximity Charge, Healing Syringe, Healing Canister, Auto-Turret
Mods, Rush, Sharpshooter, Supremo Extender
MP7
with Armor Piercing Rounds, Small Compensator, Red Dot Sight, Laser Pointer
Mods, Headshot Supremo, Gut-Wrencher, Reload All
MGL-6
with Poison Grenades, Reflex Sight, Laser Pointer
Mods, Reload All, Nimble Shooter, Gunslinger
La Varita
with Triada Mode, Killer's Covenant, Falcon's eye, Scorched Earth
Desert Eagle
with Armor Piercing Rounds, Large Rectangular Suppressor, Red Dot Sight, Laser Pointer,
Mods, Headshot Supremo, Gut-Wrencher, Reload All
The Gear is
Fuego Helmet, Hazmat Suit MK II, Prisoner's Pants, Parkour Kicks, Parkour Strap
Just stay shaded and keep cool
You can view it here