which one in particular? i mean there is not really a new "new" mechanic in M6.
The double stack is also a fire spell > stand in the water or you die (you have the same thing on Shinryu or Titania)
Even Crystal Tower had that kind of mechanic where you must stand in the water to reduce the Ancient Flare damage.
When you get the Lightning, dont stand in the water > this is as old as Rahmu from ARR.