Black stuff on my bumper? Whats this?

[BullShifter]

1st thing I would do is to fix the exhaust, it should exit BEHIND not under the bumper.

[iawix]

Regardless of that black stuff, it's probably time to replace your o2 sensor.

I have driven w/o an o2 sensor (damaged in an accident) and there is almost no difference. It's good to have one as it will lean out your mixture so your car doesn't have problems over the long haul. Nevertheless, my car still got 25+ MPG w/o it.

If you try to rub that stuff off your bumper and it feels oily, the problem should be checked out by a mechanic or dealer.

[Options]

looks like some sort of heat damage.