Going from @Rasper's post here:
I decided to do this myself and see what the results were. I encourage/challenge anyone else who's interested to do the same! More data, more better.
Here is my method and results:
Storm type: Darkstorm
I fought my current defense team of Dwarven Miner x4 in a self PVP battle. My home kingdom is Khetar for these battles in case that ends up being relevant. While I tried to get all casts done in one battle, RNG dropped enough skull matches that I ended up killing the first set of troops before I was done. The line in the results shows where the battles changed. Also the only difference between battles was that I leveled Abhorath from 11 to 18 to increase survivability.
All checks were done after the initial drop, before any matches were resolved (I finally found an actual use for AdobeAir's freeze while not in focus issue!).
Notes and Observations:
- Normally the gem spawn chance seems to be roughly 14-15%, and it's probably 14.2857% as that would be even chances for all gems.
- Under no storm the number of gems on the board ranged from 3 at the lowest, to 13 at the highest.
- Storm seems to raise the chance of the gem type dropping by about 10%, bringing it to a roughly 25% chance for the specific gem, lowering all other gems evenly by roughly 1.666r% each (10% split from 6 types), for a result of around 12.619%.