Just Cause
50 Achievements
1,000
25-30h
50 Side Missions Completed
Completed 50 Side Missions
25
How to unlock the 50 Side Missions Completed achievement in Just Cause - Definitive Guide
I suggest leaving the Side Missions until the end of the game after you have taken over all the settlements (both Military and Montano, but isn't necessary) as long as you can unlock enough guerrilla points to go up in rank to unlock a helicopter that has missiles on it.
After you have obtained a decent chopper, unlock Guerrilla Base #23 (the most southern extraction point) by taking over the military rural area just to the South of it.
Now head south from there to the Military Base, its the only one on that little southern island, its called Los Islas Defence HQ. Take over that base, check this solution by lozzy7 for tips if you are having trouble:
Now you can start grinding them, head back to the #23 via Extraction, jump in your chopper then head back to the base. Talk with the Guerrilla side mission guy (will have green arrows pointing down on him, or a green "!" on the map).
He will give you a side mission and it will NEVER have you go past the little island, he will always send you north about 800M and do something (kill a car, chopper, people, trade item, etc.) The reason you want the chopper with missiles is so you can kill car/ choppers quickly and without a hitch and not have to chase them around.
Now just keep completing them, you should be able to do one about every 1-3 minutes this way. If your chopper explodes, extract back to Base #23, and if you die you will automatically start at that #23 as its the closest base.
Keep grinding and this will eventually be yours!
So knock yourselves out! Go get them side missions!
After liberating a settlement, your guerrilla contact (green exclamation point) moves from outside of town, to standing next to the flag that you raised. When you walk up to him, press to begin his side mission. Each contact has an infinite amount of side missions, so it is possible to do all 50 from a single settlement.
One of the quickest ways to accomplish this quickly is to liberate the Island Defense HQ (the government base on top of the hill on the far southwest island). This contact works the best because none of his missions will actually have you leave the island, so you won't have to travel very far. So get a hold of a Chimera, a Skreemer, or some other fighting helicopter and travel to this contact. Land right next to the flag, get out, begin your mission, fly to the target, retrieve/kill/destroy your target, and fly back to the base. Do this 50 times to complete this set of achievements.
Completing missions for this contact will also improve your relations with the guerrillas, which will move you 1,500 points closer (50 missions x 30 points each) to getting the Chimera to appear at your safe houses.