Is my head gasket blown?

My car was losing power, and bogging down. Then the low coolant light came on and I thought that was odd because I remember a friend of mine just added antifreeze. I went to add more to the overflow, and I realized that he added old green antifreeze to dex cool. I checked the radiator, it was empty but a mud like substance lined the neck.

I assumed that was the reason it was running bad. I bought flush kit and prestone super flush. While I poured the prestone in, and let the car heat up, the engine stalled. I then tried to restart a few times, and failed. There was a strong rotten egg smell, white smoke coming out of exhaust, and water near tailpipe. I continued to flush with radiator cap off, it appeared to run clear almost immediately.

After a bit, I tried to start again, and it seemed to want to, but I think my catalytic converter is clogged severely.

I checked the oil, it didn't look out of the ordinary. I pulled a spark plug and it looked wet and maybe a bit of oil? I assumed it was wet because it was flooded.

Previously the car didn't leak oil or antifreeze. I am not sure where the antifreeze went, if it gelled up in engine, but then why would the water run clear during flush?

The car will not start still.

Any ideas or suggestions on what to do?