I've a question. If I have a Demon's Scourge and a Ryu's Ashura Senku in play and then I play the Form in Blind Stance does my opponent lose endurance equals to his hansize +1 or his hansize x2

I would think it's handsize * 2

RAS makes them burn for 1 after each card they draw (several seperate burns of 1 vitality each)

Demon Scourge makes them burn for more after every time they lose vitality due to one of your card effects

So, with both RAS and DS active, your opponent will lose 2 vitality for each card they draw. Additional RAS'es will double the burn damage each time.

I must compliment you, that is a great combo.

I should also add, that it is YOUR hand size X 2 that your opponent loses, due to the wording on ashura senku.