I took my car to a mechanic for my check engine light. It came up with 9 codes. P0455, P0172, P0302, P0304, P0305, P0300, P0301, P0303, P0172. I have replaced all the plugs and wires and whatnot. (not sure what the rest of the things are called) These codes still come up. What could it be?

Means it's misfiring and it could be due to low fuel pressure, plugged up fuel filter, bad ignition coils (depending on type of vehicle).

I believe the rich mixture code 172 is also based on a vacuum leak. Mercedes is known for using lots of vacuum control. Are any of the controls acting up. The 455 is a gross emissions leak. Could be the O2 sensor coming apart on the cat/converter. It sounds like you or previous owner drove this alittle hard. Did all the codes for misfires (301..etc...go away? Also. Check battery and alternator condition. One problem usually causes the next. Hope this helps

All the P0300 codes are engine miss codes. The P0455 is a catalyst inefficiency code and the P0172 code is a rich mixture code. All of these could be caused by faulty oxygen sensors. What kind of car, engine size and mileage is it?