Black soot on the exhaust pipe of subaru forester sg5 turbo

There's three things I can think of:

1. Bad tune
2. A stuck injector, or
3. You've got a leak in your charge pipe.

Soot indicates too much fuel (or conversely not enough air). If you don't find any leaks on the charge side, the mapping in your tune is dumping too much fuel, or you might have a stuck injector, also dumping too much fuel.