Found at Guerra’s Nightclub, duh. The northeast part of the starting island. He is at the bottom level in the parking lot, in the back of his club, on the south end. You can go around the outskirts of the club and you will find a big rock on the south side. You can scale this rock by finding the protrusion next to the sidewalk, under a blue thing. Basically, this will cause you to drop right next to the boss and finish the job quickly. 
But fighting your way through the denziens out front is not a bad idea since you are lacking skills. They shouldn’t kill you, but be sure to kill anyone shooting at you. You will go through the front, kick open the doors to the back, and then make your way to the boss.
You will find that the bosses are just like the other enemies, they just have more life and they have all their minions. Guerra, like all the other bosses, can be killed with grenades. Since you don’t have the big guns yet, just keep chugging frags where ever the boss is. He’ll be dead in no time. ———
With him dead, there is another supply point nearby; in fact, you could have got this before the boss (doesn’t matter).
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Supply Point:
Royal Vista
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If you are at the last boss’s place, just run north and start hopping up the blue building to reach the point. There are some enemies up here, but nothing special, and they never are.
However, if you not in the jumping mood, or you simply can’t get up there, then there is another path. Go to the intersection near Guerro’s. Take it west, to the front of the Vista. You will eventually see a red covered walkway above the street, go up the stairs, cross the walkway, and then take either way to attack the goon protecting the point.
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Okay, now let’s go get another supply point to the southwest of this one. I would advise trying to reach it by hopping buildings, just to nab some agility orbs. And you could get the nearby boss first, it doesn’t matter.
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Supply Point:
Hillside Housing
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Attack from the street that runs west of Royal Vista. When you near the point you are also in the midst of the nearby boss. You can kick the gate open, or just hop up the buildings at or around the building with the point. From up here you can take out all the enemies and reload before you set out, though, that may not be necessary.
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Well, you are basically already fighting the boss’s goons…
