Even just cursory tests show that Fizzbang is not actually 50/50 explode versus buff. Not for me, not for the AI, never has been. Explode I’d put at at least 2/3, possibly even 3/4 of the time, but I haven’t gathered enough hard data to confirm. The description is just not clear on this, and most people assume since the text says explode OR buff random stat that each one has equal chance to happen. Spooky Imp is an example of where they have done this before with another OR spell, as the description states it will transform a random enemy OR give all allies magic, but is actually 2/3 magic buff and 1/3 transform.
(source: Knight Time - #40 by Sirrian)