For what it’s worth, I really liked that concept (drop bear). We don’t have enough of the “player-weighted RNG” that I think strikes a good balance between a sure thing and a braindead coin toss.
Another take on that spell:
Destroy a random column. Deal [Magic + X] damage to the target enemy, boosted by Green gems destroyed. If no Skulls were destroyed, instead take 10 damage. [5x]
Effective use of the spell would require you to wait for a greenish board with a relatively even spread of Skulls. Would potentially go nicely with Forest Guardian.