~ All the slots are with 96% RTP and they don't change with the promos or with the casinos .. so forever 96% 
~ and the RTP is always de same 96%, never change 
Thanks for your replies, but how would you comment on these words on bitcoincasinokings site about Windy City by Endorphina?
"There is also a Double Up feature, where you can double your winnings. The Return to player rate is only 84 % in this feature, so ..."
Is it true? And if yes, are there any other features on Endorphina slots with which we can get a different RTP than 96%?