Above post bad check valve can put a Merc down. IMO that could have been your cause with possible others. 2 stroke outboards do not like to run lean period even for short periods of time.. 5 common issues we see with Mercs that was the major cause of engine damage is

1.A fuel related issue leads into lean to very lean running conditions
2. then leads into detonation
3. Merc oil pump failure
4. Improper cooling / overheat
5. the check valve stuck, restricted or failing

1 thru 5 practically in that order of how they failed..

Which check valve? The check valve in the oil system which is by the oil tank on the motor?

If it was a dirtbike motor I would lay odds on an air leak.

Tough to argue with the spicnspan condition of the top of that piston though..Water in the cylinder and finally ingested to much and hydro locked and snapped the rod?

Look at all the corrosion present on the bottom of the cylinder head mating surface and also the cylinder above is getting some wash to it also.

Got a pic of the head before it got cleaned up?

just my 2 cents many on here that know more

I would also say that it leaned out somehow. One thing also is to check your fuel lines. With ethyanol it can cause the inner wall to collapse. The mechanical pump is weak that supplies the fuel can/electric pump. Depending on the age of the hose I would replace it anyway.

I took the entire fuel line off that goes all the way to that motor, turn hose on and water flowed through the hose without any restriction whatsoever. I was able to eliminate that as a possibility but i thought the exact same thing. Again I thank everyone responding and the knowledge everyone brings.