Head to Cauda in the southwest and speak with Sheldon in Contrabandero. Before you head out, pick up a Fire Leech from a Rebel Drop if you’ve got one available. The Fire Leech makes this mission much easier for you. After the cut scene, take out the enemies that attack while keeping Mario and the EMP safe from harm.
Focus on the soldiers in front of the base as you make your way toward the mounted gun marker. Use the gun to make quick work of the enemies unfortunate enough to cross your path. As the battle continues more and more enemies attack. If the mounted gun isn’t enough, commandeer one of the enemy vehicles as an alternate method of attack.
When the helicopters show up, grapple up to the choppers and remove the pilots. If you’re not good with the grapple, you can use one of the anti-air guns near the river. Once the EMP nears a full charge you’ll have to deal with paratroopers from above. Continue to engage the enemies as you start to move back toward the EMP.
Once the EMP is done charging use it to disable the remaining enemy vehicles, then restock your ammunition while you have a moment. Grab the minigun and hop into one of the vehicles, then continue to take down the enemies that are parachuting in. Stay on the move to avoid the red circles that indicate where their attacks will hit.
Head back to the EMP and use it a second time to clear any remaining vehicles, then take out any soldiers that are still giving you trouble. There may be a tank near the end of the cave, so head down there and take control of the tank if it’s still functioning. The tank makes the next wave of enemies much easier to deal with if it’s available.