Alright, first of all, I love this. I love all ideas around super unique and custom Kings.
Making an Ice King would be pretty simple, Make a box 9cm by 30cm and 9cm deep. Fill it with water and let it sit outside in the cold. Freezers may be difficult for this, just because they will be slow to freeze that much water. Outside in a cold day will probably work better.
Snap the frozen block out and then carve as desired. I have a chainsaw, which I believe is the preferred way of carving ice. I bet we could get one king out of ice and still have all fingers and limbs intact.
Now, here is my worry though.
A King is 0.0858 cubic feet in volume. One cubic foot of ice weighs 57.41 lbs. So, this ice king before any carving will weigh 4.93 lbs. In comparision, ash wood weighs 42 pounds for a cubic foot. The same block of ash is 3.60lbs. That extra 1.3 pounds may make it problematic to knock down. (The other ancillary concern would be the king freezing onto the snow beneath.)
Now, if you can hollow out the inside with a 5.5cm by 5.5cm by 21.2cm empty cavity in the ice (removing 1.3 pounds), you would have a hollow ice king that would weigh the same as a typical ash wood king. Plus, if you hit it hard enough it may smash into peices which would be awesome!