If you give a Destiny Knot to one of the two Manetric (as suggested by Meloetta), you guarantee 5 out of the 6 IVs to be passed down from either parent to the offspring. This means that only one IV needs to be correct for the HP Ice to be passed down. The chance that this will happen is 1/2 (because IVs range from 0 to 31), which means that
If you use the Destiny Knot there is a 50% chance of the HP Ice passing down.
If you don't use the Destiny Knot, 3 IVs still get passed down for either parent, which means that the probability is 1/2^3. So,
If you don't use the Destiny Knot there is a 12.5% chance of passing it down.
Hope I helped!
