You only get to use that mana on opponents turns, but still thats usually when you want to use it anyways
Not only does it provide treasures and creature tokens every turn, it also gives you pseudo-card draw
For example, Amber/Emerald decks are mostly focused on discarding the opponent's hand, but Emerald/Steel decks arguably do the same thing better
For X=6 (14 mana), you can force a player to draw 64 cards, which is often enough to take someone out of the picture, and X=7 (16 mana) guarantees one opponent has to pack it up
He plays well off the theme of raccoons, making trash worthwhile, but his ability to turn artifacts and enchantments into indestrucible card-drawing engines is pretty incredible
If all Cankerbloom did was blow up an artifact or enchantment, something youll have no trouble finding on green creatures, I wouldnt give it a second glance