I was playing the boss Morty and using wynaut with shadow tag as the first pokemon to kill the mega gengar, however the gengar in form managed to be changed and when I was in froslash my game froze and crashed giving me defeat against the boss. How to proceed with this problem?

Hello @Kbary
 

Thank you for your report, and I apologize for the inconvenience you've experienced with this interaction.
 

The described behaviour of Gengar being able to switch out on your Shadow Tag Pokemon is not a bug, but rather the intended behavior as Ghost-type Pokemon are immune to the abilities effect.
Regarding the game crash, we can't do anything.
 

Feel free to reach out if you have any further concerns or questions.
 

Greetings, ~Crimsonhound

Unless it's a new update, this behavior of Morty's Gengar wasn't happening, because being a ghost type, he was using shadow tag and he never changed it.