The Incredible Hulk

This is the southern most Enclave sector and once you get them to Phase 3 you'll fight the the building some shielded troops and then finally the leader who weilds a purple hammer. He can only be harmed by Thunder Claps that use the Rage meter for a widescale damage strike.

This bosses special moves revolve around hammer swinging and shooting homing energy balls at you.

This solution applies for all 4 Enclave group achievements. In order to destroy a group you need to let the group evolve from Phase 1 to Phase 3. Each group controls one sector of the map. As the game progresses, you will see a purple dot on the map, one for each Enclave group. They will all be in Phase 1. You need to take each group to Phase 2. If you hit the back button, and then LEFT on the D-Pad, you can move to the ENCLAVE screen, which will allow you to see all Phases available for each group, along with the progress bar, which will be white and needs to turn red. Once the bar is red, then the group will be available to evolve into the next Phase. This will not happen automatically. In order to turn the bar red you can do the following:

Option 1: As you play on a particular sector, the group controlling the sector will eventually appear. You will see a red banner below saying something like "Warning. An Enclave group is active in this area". When this happens, you will see a few Enclave soldiers show up. You should stay away and let them do damage to the city. This will raise the bar to red.

Option 2: This other option is a lot easier and faster. You can replay a previous Phase (phase 1), over and over again. Each time you do, the bar will raise. These fights last 2-3 minutes.

Once the bar is full, you need to hang around the area controlled by the particular Enclave group you're trying to evolve. Get to Alert Level1. You will get the "Warning" message first. Just let them be, do something else, like going for collectibles, or hang out in some roof, but do not go into missions, mini-games, or anything that may interrupt them from damaging the city. If you choose to go hide on a roof, make sure the Alert level is still on 1, so you don't get any flying enemies. Go get a sandwich and come back. Eventually you will see a message saying that "the Enclave group has finished production of a special weapon". When this happens, a new purple dot will appear on the map for that Enclave group, and it will be Phase 2. Do this for all 4 groups.

For Phase 3, do the same. Keep playing Phase 1 until you raise the bar. Then go to the particular sector, get Alert 1, wait for Enclave to appear, hide, and wait for the 3rd dot (Phase) to appear on the map.

I did all this after completing all the missions, so you can do it that way too. When fighting the bosses for each one (they are all similar), do LT to lock on target, Jump and X, to hit it in the air. When he comes down, you can hold Y for charged hit, and you can also hit buildings to raise the bar and do an all out Thunderclap (with maximum rage bar). This will do a lot of damage.

I also got all the groups from Phase 1 to Phase 2, before moving any into Phase 3. It doesn't have to be that way, but I had no problems with it. You could get a group all the way to Phase 3 and eradicate it, before moving another group to Phase 2, I guess. But I didn't do it that way.

After beating the boss for each Sector, you will get an achievement. After beating all 4, you will get Para-Gone, another achievement. After you are done with all these, Save and Quit, come back into the game, get to Alert 1, and beat 1 enemy. This will unlock Veni, Vidi, Vici achievement.

Hope this helps.