Question for mechanic Hi guys,
Today I had somewhat amazing(?) experience.
So the student started the engine like normal and we leaned for the taxi all that fun stuff.

We were about to get the ATIS info then, all of sudden engine was experiencing violent vibration. I checked EGT and changed mag selection both to left then right to see if spark plug was fouled. Vibration was less but still there with one mag. If spark plug was fouled usually one of mags makes engine run smooth. I checked EGT #2 Cylinder was dead like super dead EGT wasn't up at all and CHT was almost none as well. 

Any thought?