Numbing Cold (su)
When an ice elemental deals cold damage to a creature, that creature must succeed on a Fortitude save or be staggered for 1 round. The save DC is listed in the elemental’s stat block and is Constitution-based.
Whats happens if an opponent fails 2,3,4 hits in a row?
If they are hit multiple times during one round, you mean? They're still only staggered for 1 round (the duration doesn't increase).
If they are hit next round as well, and continue to fail, then they'll continue to be staggered.
At most it would seem like the duration might stack. I can find no precedent to move staggered to stunned. As the ability doesn't expressly say that additional hits add to the duration (such as Staggering Critical or Stunning Critical) I would say that each failed check staggers the creature for 1 round, with all of them occurring concurrently.
So the creature is staggered for 1 round, further failures basically do nothing.
Thanks for your thoughts and I agree..one round.