He is on a building that is connected to a building that acts like a bridge from the streets. The main entrance is from the north of the Hillside Housing, behind some gates to the Hillside Housing (If you got the third supply point, then you are already in the area). Or you could use the more creative points of attack, which all countless.
There will be a bunch of goons around the main building, but just make your way to the surface between the two colored tops: the red and blue tops. He is on the tiny bridge between the two, and there are a couple of higher ranking goons at his side. They just have twice the life of normal, regular bad guys, so nothing big, but do kill them first. And then you can just run up the steps and beat him to death.
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Boss 4 is closer, but why not cross the city by rooftop to get some more agility orbs? Okay, I did it backwards, but it would work either way no matter who you take first.
You should know that you don’t have to do everything I say in the order I say, and don’t follow to a T, you can go get orbs or whatever between the main action.
Get the next supply point before taking on Violetta, no matter what.
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Supply Point:
Social Security
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The easiest way to get to the top of the building is by approaching from the highway on the north side. Hop the fence (by using the small beam in the middle of the fence), get on the support for the highway that almost touches the building, and then climb the windows directly to the point.
You could use the smaller buildings by the La Chica Loca on the east as stepping stones to the point, but that means cutting through a bunch of thugs.
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Cross the street for the nearby boss.
