There is very little RNG here, even though it's got the word "random" on it.
In the vast majority of cases, it's going to clear the board, period. If the Shaman has minions, he's going to trade them before playing Volcano. And since it can't hit face, there's nowhere for excess damage to go.
Provided your board is empty, this card is considerably stronger than flamestrike. 15 damage will usually clear pretty much any board the apponent has. Plus this card works as a secondary hard removal for big minions.
it removes 15 health from the board guaranteed. That seems pretty reasonable to me.
I mean, it's basically a slightly different spin on Elemental Destruction. The decks that would use Elemental Destruction would use this. But since Control Shaman isn't a thing we don't think about it.
If control shaman becomes a thing, you can bet this will probably make the cut.
I thought my control shaman was dead now it lives on yay, no excited to decimate aggro with this. You guys realize that since this card does 15 damage, more with spell damage you will always get to clear the entire board if the sum total of the health of all minions is 15 or below, I love it, better than elemental destruction in the early game only.