The Mattress

So, in the games, the Reveal Glass is just an item for the player to use in order to transform the three Forces of Nature into their Therian forms, based off the Demon Detecting Mirror from Chinese mythology. In the Best Wishes anime, however, it's an Eldritch nightmare!

First, let's compare it to the most obvious parallel: the Red and Blue Orbs from Hoenn that control Groudon and Kyogre. While it works in a similar fashion with the Forces of Nature, there is one major difference: the Orbs were man-made and hold no sentience whatsoever. They were created specifically to control Groudon and Kyogre as weapons of aggression, with it backfiring when the link created between human and Legendary Pokémon causes said Legenady Pokémon's aggression to feed back into the human and drive them mad. The Reveal Glass, however, has no defined origin, seems to naturally co-exist with the Forces of Nature and Meloetta, and is sentient, responding to spoken words from its human wielders.

And yeah, about that Meloetta. She serves two important roles here: her song is the only thing that can break the seal of the Reveal Glass whenever it's locked away, which she has to sing from some monolithic keystone device, and she is the one the Reveal Glass' power must flow through and into the Forces of Nature. For some reason, she with her pure and innocent soul is the only being who can handle that power. If a human wants to control the Forces of Nature with the Reveal Glass, they need Meloetta to be the channeler of its power. And while Meloetta's original position had her do this willingly for the rulers of Abyssal Kingdom, she can also be made to do it by force...as Giovanni of Team Rocket so ruthlessly displays.

Just look at this shit. Not only are the minds of the Forces of Nature being forcibly controlled as per Giovanni's designs, but channeling the Reveal Glass' power against her will seriously looks like it hurts Meloetta physically and mentally. And that red glowing circle on the ground beneath the Reveal Glass is downright Satanic (between Giovanni and Ghetsis, the evil team leaders in Best Wishes had a thing for glowing Satanic circles on the ground and glowing red eyes of mind-controlled Legendary Pokémon. Giovanni did it a lot cooler and scarier, though.)

And then we get the most terrifying part of this whole thing. Remember when I said only Meloetta can channel the power of the Reveal Glass that controls the Forces of Nature? Well, let's see what happens when it's channeled by the human instead! Take it away, Giovanni!

The same glowing circle that's on the ground is now on Giovanni's forehead and his eyes are red, because now the Reveal Glass' power flows directly through him and not through Meloetta. And as I said before, the Reveal Glass appears to be an entity unto itself that co-exists with Meloetta and the Forces of Nature, meaning its power was never intended for humans. When a human absorbs and takes control of its power, it drives them mad...again, similar to the Red and Blue Orbs from Hoenn, but with a huge, far more horrific difference.

Giovanni's goal turns from conquest to destruction. But as Ridley confirms, this specific brand of madness isn't coming from the Reveal Glass nor (as with the Red and Blue Orbs) from the controlled Legendary Pokémon. It comes from within. The Reveal Glass is a mirror, and it reflected back Giovanni's own id (in Freudian terms) into his mind. Destruction was always Giovanni's most base desire; his id is all about the desire to crush others with overwhelming force. It's just that usually his ego steers it toward the rational objective of conquest, with his superego seeking that for the rational objective of ruling. When both the ego and superego vanish as they do now, there's nothing left but the evil primal beast lurking at Giovanni's core.

But here's the kicker: Giovanni wanted to conquer Unova and then from there move on to conquer the world. Now he wants to destroy Unova...so what do you think he'd want to do to the world afterwards? And a scarier proposition: what if Giovanni got killed in the crossfire and as a result the Reveal Glass' power...didn't return to it? And the Forces of Nature were permanently stuck on the destruction command? This was a short but incredibly tense moment when you consider those factors, and it was only Jessie, James and Meowth's quick acting that knocked the power back into Reveal Glass and restored Giovanni back to sanity.

Fun fact about this music; it only played twice in the entire series.

The first time was in BW007, when Giovanni is telling Jessie, James and Meowth of the existence of a "mysterious organization" in Unova and warning them that they may already be aware of their criminal activities. The pay-off to this was meant to be in BW023, and I suspect this music would have played again in this scene where we are introduced to Team Plasma:

But since the episodes get postponed and then banned from release, this didn't happen. Instead, the music plays way later at the very start of BW114, in - you guessed it! - Team Plasma's debut scene. An audio cue to confirm this group is who Giovanni was talking about.

Unfortunately, the international dub did not use the music on that second occasion despite having done so for the first. This in addition to outright retconning the general story, not just the episodes, of BW023 and BW024 from canon*, meaning that Giovanni's warning to the TRio, like most of the Meteonite mission beyond Dr. Zager's debut, was rendered pointless.