Question

MindStone

If you get a four star from grandmaster does it decrease your chance for the next one?

Solswerd

Nope...each crystal is an individual pull. That is why someone can open 100 PHCs and end up with zero 4 stars or four of them. (regardless of the stated 2% drop rate) Someone else opens 4 PHCs and can get two 4 stars. It is random.