MArcomage

Sulfur Rain, uncommon, 8 gems
Burning; Quick
If the enemy increased his Stock last round:
Enemy Stock: -8
else:
Enemy Stock: -4

The base effect of this is already very strong. You're reducing your opponent's resources by a likely 12 at a cost of 8 gems. It's roughly on par with Pyrobolus when its extra condition is met, which is only a Common, so this value is probably balanced in that way.

I wonder about this card's conditional effect, though. The condition, which is potentially unavoidable in most decks as there are numerous cards that give a resource or two in addition to doing something else primarily, causes a probable loss of 24 resources. I wonder if it shouldn't be less, perhaps 5 or 6.

When i thought about it, i have to see that the effect is quite strong. I will change the condition and the stock reduction.

Id call the change overcompensation.
This way there are really few cards that trigger the condition.

It would take a huge bite out of Bank and Alastor, to name two off the top of my head.

Edit: I think the conditions have changed again since I last looked.

Is the 12 you mention an overall increase of resources or just a particular resource to be increased by 12? (i.e. would you consider a stock+4 increase to be the 12 resources, or a +12 gems for example to be the 12 resource).

If the first case is considered then it's still pretty easy to meet the conditions (Vampire Queen, Bank, Fairy, Angel, Saint's Day etc. plus other cards like Dark Foundry, Dark Forest, Mountain Sentry etc.)

I consider both as an increase of 12, either stock +4 or gem +12, this would trigger the effect.