I've been seeing a sub for several months and running out of ideas for new scenarios. Any ideas to spice things up?  We've done just about everything except not into causing extreme pain or humiliation. Just asking...

I have gone through several drafts of what to answer.

Been seeing the same Dom twice a month for 3 years and she never fails to amaze me.  Your lazy or no imagination.  Just my thoughts

I played with a sub for a few years. Every Saturday was punishment day.  She would kneel in front of me, naked with a collar and hands fastened at her sides to a leather belt.  I would look down at her and we would review the week and how she had done at her chores snd pleasing me etc.  After the summary and her apologies for any failings and a period of begging for mercy, I would decide the punishment.  It was always a spanking with either hand, or paddle or paddle with hole (so more painful) etc. I would write a number down which represented the number of packs and put the paper aside.
She would have to guess how many I planned to dispense.  If I had planned on say 12 and she guessed 15, she would get 15 so 3 more than I had planned.  If she guessed the correct amount, 12, she would get that. If she had guessed low, say 9,we would double the amount she was under and I would add that to the 12. so 12 + 3x2=18. If the smacks were to be hard and I was using the paddle with holes, the extras were meaningful.  
She would tell me her guess and I would look in her eyes and stroke her cheeks and kiss her  then, after waiting a little, I would show her the paper with the number I had decided written on it.  
The she would have her collar fixed on the floor at the right length for her to lie across my lap.  I would hold her legs in placed with one of my legs, I would insert a thin rectal dildoe to hold ass here in place, and would deliver the punishment.  
We had other games like this around punishment.

several months not years...

That sounds interesting. I think I'll try it. Thank you for a constructive comment. Any other ideas feel free to pass along to this novice...

So hot

Thanks for suggestion. Fun times...