All my Dragonvale posts are being Indexed HERE for easy access.
The next limited dragon is now available in the Winter 2020 event in Dragonvale. And it has a specific breeding combination.
Snowpocalypse + Shiver
Snowpocalypse adds Plant, Earth, Cold, Lightning, Air & Metal elements, and Shiver adds Cold, Air and Light. This means 7 elements are in the breeding pool, which makes an enormous number of possible offspring.
There is a total of 228.1% set breeding chances among the 92 possible dragons. So no regular dragons will be bred, and the set % of the rare, epic and limited dragons will all be decreased by more than a half. The 1.5% chance of breeding a Snowball will be decreased to 0.66%. This means 106 breeding attempts will be necessary to have a 50/50 chance of getting one. This multiplied by the average fail of 16.48 hours, means 72.79 days of non stop breeding will be necessary to have an even money chance of breeding one.
To put it another way, this limited will be available for 7 days, or 168 hours. Dividing 168 by 16.48 means 11 attempts on average during the week. This will give you a 7% chance of breeding one with this combination. Or more importantly, a 93% chance of not breeding one.
Cloning a Snowball
The Snowball dragon gives only 2 substitute elements when breeding, cold + air. The shortest dragon breed time with those elements, is Snow, at 8 hours, so you should use that when trying to clone for one in the Cooperative Breeding Cave.
Snowball has a 4% chance of cloning in the CBC. Nearly 80% of the fails will be Snow and Blizzard, with the rare Jetstream and Derecho taking up the remainder. 17 breeding attempts to get to a 50/50 shot at cloning a Snowball, or 6.21 days. 7 days non stop will equate to 20 attempts, or 55.8% chance of cloning a Snowball in the CBC.
Cloning a Snowball adding Plant
Just to check, I did some calculations if I added the plant element to the mix.
Reindeer is the shortest breed time for a plant/cold/air hybrid. But its smaller % for breeding and cloning meant that Lichen was actually the better choice as the second parent. The 4% chance of cloning a Snowball is the same, so it remains at 17 attempts to get to a 50/50 shot. But there is a slightly longer average fail time, which decreases the number of attempts during the week, and does give the chance of a 48 or 60 hour breed. Whilst you might find it more palatable to spend gems speeding up the 1 in 6 breeds that would be a Lichen, the recommendation is to clone Snow with Snowball.
Good luck.