Thinking of this capability like a miniature form of the Mutate mechanic is sure to help people to understand the mechanic a bit better
If exerted be that through singing, questing, using one of their abilities or other reasons in another players turn these characters can be challenged, requiring the challenger to exert their own card and then resulting in both characters simultaneously applying their strength to their rivals willpower
The only thing you have to worry about is Exeggutor's Big Eggplosion attack
If an equipment becomes a creature, its subject to the same rules governing creatures
As ridiculous as 900,000$ sounds, to someone as rich as, say, Jeff Bezos (an extreme example), 900,000$ is like the average person spending 900$