Oh yeah, I actually knew about that! It was to the point that me and my friends would race at the start of each match to get the Wario cap first. And typically, whoever kept the cap until the end won.

Wario was beyond broken, essentially.

This happened to me once, and it gets even worse. The same glitch may occur during the game's boss rush mode, forcing you to redo the entire thing for another shot at the hidden superboss.

Not sure if I could consider myself extremely lucky for encountering both in one playthrough. 🙃

So unfortunately I'm still stumped as to what causes Fury, but I've at least figured out that the status has a chance of fading on its own after a few turns, also seemingly at random.
But I'm still determined to solve this mystery eventually! Certainly it can't stay hidden forever! 😁 (5/5)

The first time it took a total of 969 damage (12 hits) before Fury activated, but the second time it took a whopping 1273 (16 hits) instead.
After a bit more trial and error it turned out that it also didn't matter how much damage he took at once or if he was at low health or not. (4/5)

Two times in particular I've been fighting a Crawful alongside the Beehoss, but I only let the bees ever land a hit. Both times Bowser took damage with an active defense buff on the first hit for 57 damage, but every following hit dealt 76 damage. But then the first inconsistency happened. (3/5)

First off, I've been playing the original version with the stats shown below. I also have Luigi wearing the Challenge Medal to make enemies a little beefier. Lastly, I've been fighting Beehosses to keep both Bowser and the enemies alive for as long as I need to. (2/5)

I'm actually tempted to try one myself now! Most of those I actually already did myself except for the first one (always upgraded Stache instead) and maybe items from minigames. Thank you for the idea!