I used to have shadow ball, sludge wave, taunt, focus blast on all 3 of my gengars.

I have been unable to teach any of them sludge wave.

 

 

I tried replacing the moves with all tm/relearner moves before teaching as well with the same result:

 

Is there something I am missing?

Hello @DeIta. My apologies for the inconvenience.

 

In Generation 7, which PRO uses, Gengar is only able to learn Sludge Wave through the use of an Event Move Tutor, which is located in Celadon City's Game Corner.

Speak with the TM Teacher and she will offer the option of the Event Move Tutor for 15k. Gengar should be able to learn it this way.

If you have any further questions, please let me know.

21 minutes ago, Epithet said:

Hello @DeIta. My apologies for the inconvenience.

 

In Generation 7, which PRO uses, Gengar is only able to learn Sludge Wave through the use of an Event Move Tutor, which is located in Celadon City's Game Corner.

Speak with the TM Teacher and she will offer the option of the Event Move Tutor for 15k. Gengar should be able to learn it this way.

If you have any further questions, please let me know.

Thank you, that worked! 

Glad to see it worked. Since your issue has been resolved, this thread will be closed.

If you have another question or concern, feel free to create a new thread.

Have a great day.