There are some points in your comment that I want some clarification like:
1. You said after clearing dark dungeon (or is it frozen castle of death?) I must not click "retry" or replay button so that the special stage will come more frequently.
And if I click replay or retry, the stages will refresh and the special stage will not come again faster... Is that what you mean?
So in simple terms, I must go to main lobby each time I clear a dark dungeon stage and if I wanted to play dark dungeon again, I must do it repeatedly to access frozen castle faster... is that it?
2. You said "That stage comes twice even thrice just after another" does it mean that frozen castle of death comes at you twice or thrice in 3 straight rounds to have a chance of acquiring dark sword and after that it will not happen again for sometime.
That twice or thrice chances didn't happen to me. I will try what you said bro, I will just save enough stamina and potion. Forgive me if I didn't get it straight, I just want to understand better. 🙁