Spoilers of course.
From the astonishing Pinderpanda.
What does it mean?
Note: Batman RIP is polysemic, ambiguous, elliptical and all those other things that're great for literature and troublesome for bald 'fact files' like this. The section that follows therefore cannot aim to be as 'definitive' as does the rest of the guide, but can only aim to be plausibly interpretive.
What do the red skies mean?
Red skies appear on a number of occasions throughout Morrison's Batman RIP.
In the opening 'flash forward' sequence to events six months after the main storyline, over the skies of contemporary Gotham as Batman pursues 'The Green Vulture', during the sunset Honor Jackson shares with Bruce, and during Bruce's subsequent transformation into the Batman of Zur-En-Arrh.
Red skies have a particular meaning in DCU-lore. They were first seen during the Crisis on Infinite Earths, most notoriously in what became known as "Red Sky Crossovers" - issues marketed as Crisis tie-ins which had little connection to the storyline other than that particular colouring choice.
They are now a familiar omen of disaster. As DCU#0 puts it, "When the Multiverse is on the verge of destruction, when the skies drip red as the barriers between parallel universes bleed... When Earth's greatest heroes rise up together, willing to sacrifice everything they have in defense of all they hold dear... That war is called a Crisis."
2006's Ion maxiseries eventually revealled that the reason for this is that the weakening of the walls between universes during times of Crisis allows for a glimpse of 'the Bleed', an arterial channel between realities first introduced in Warren Ellis's Stormwatch run which went on to become a major part of the cosmologies of both Wildstorm and Final Crisis.
The association of red skies with Crises raises the question of RIP's association with Final Crisis. Addressing this in an interview Morrison says, "it could be the start of it, because those red skies have been seeping in for a while, but it's certainly not happening at the same time as Final Crisis #1. It could be happening a week before or something, but I haven't exactly specified it." (IGN, August 2008 ). So the red skies should be seen as signs that the Final Crisis was immanent, rather than that it was underway. This fits the sequence of events in the story.
This leaves the red skies in the six-months-later 'flash forward' sequences however...
"That's actually even more in the future than Battle for the Cowl," says Tony Daniel, "[That] would, hypothetically, appear at the very end of it" (Daniel, Newsarama, December 2008).
This places them well after the conclusion of Final Crisis, and would seem to suggest that on that occasion a red sky was simply a red sky.
Red also has a significance (or at least a significant lack of significance) in the red and black pattern the Joker is making throughout the story. The red skies also serve as visual references to this.
How exactly did the Joker talk with his tounge sliced in half?
In Batman #680 the Joker reveals that he knows Doctor Hurt's true identity by mutilating himself to display a serpent's tongue. It has troubled many readers that he appears capable of comprehensible speech after doing so.
It is however entirely possible that the Joker wasn't capable of comprehensible speech before doing so, and the tongue slicing merely serves to make this explicit.
The Joker was shot in the face in Batman #655 and, when he reappeared in #663 had undergone facial reconstruction surgery leaving him incapable of producing any sounds except "a subhuman paste of of slobbery vowels and clicking consonants." The prose story in that issue makes it very clear that, while the Joker thinks he's talking, all that's coming out is "mangled phonetics and toxic intent."
When this version of the Joker reappears in DCU#0, Tony Daniel draws him with retracted lips which would be unable to manufacture any rounded vowels or labial/labio-dental consonants. Daniel is careful never to actually show him speaking.
It seems very likely that the Joker we see in RIP is talking in the same "subhuman paste" and that his speech balloons (coloured green to distinguish them from conventional dialogue) contain the words he's trying to say rather than the actual noises coming out of his mouth.
Careful reading of the arc shows that nobody, from the Arkham psychiatrist, to the Club of Villains to the members of the Black Glove, show any sign of understanding him before or after the tongue-slicing. They respond only to the fact that he has spoken or to actions that he's taken rather than to the content of anything that he has said. There's no evidence that any characters with whom he converses in Batman RIP can makes heads or tails of what he's saying.
There's one exception to this.
The Batman of Zur-En-Arrh has an extended and two-sided conversation with the Joker, and is able to fully understand him both before and after the tongue-slicing.
But then, the Batman of Zur-En-Arrh also has two-sided conversations with gargoyles.
Batman typically works by gathering evidence and consciously interpreting it. In RIP we're shown that as the Batman of Zur-En-Arrh this process is unconscious. Whereas normally he'd read the city and deduce what the clues were telling him, in this state of mind he experiences this as direct linguistic information; "Shh! The city's talking" (Batman #679).
It follows then that he'd also be the only one able to converse with the Joker. Just as he interpreted the city's clues and experienced them as talking gargoyles, he'd be able to read the Joker's body language, intent and phonetics and experience them as actual speech.
It's also worth looking at what the conversation is about. The Joker is insisting that all life is fundamentally meaningless and that all attempts to make sense of it are doomed. And the World's Greatest Detective is making a liar of him...just by the simple act of understanding it.
Who (and why) was the Black Glove?
At San Deigo 2008 Grant Morrison said that the Black Glove's true identity would be someone "everybody in the world knows." Curiously, when the identity was eventually revealed, much of the readership failed to recognise him.
Lets go back to when Morrison first took on the Batman monthly and he mentioned that he'd "rather Batman embodied the best that secular humanism has to offer" (Newsarama, 2006). This take on the character has proved vital to how Morrison has written Batman throughout his career and is crucial to understanding why the Black Glove is who he is.
By 'Humanism' here, we're talking about the whole raft of philosophical ideas that came out of the Enlightenment and told us that it was possible for us to stop thinking of life as one long downhill ride from the Fall or the 'Golden Age' and to start thinking that humans had a chance to improve the world and themselves if they started playing smart and making the effort.
Where Batman comes in is that humanism does this through reason, rationality, science and all that sort of stuff, to the exclusion of all the irrational mumbo-jumbo that's also a part of being human. Arkham Asylum, by a younger and angier Grant Morrison, punishes Batman for his humanism by painting him as a repressed, joyless prig and having him suffer humilation and agony for his failure to integrate into himself myth, ritual, chaos, the Id, and all the other things reason excludes.
By the time of Morrison's JLA run things are very different. Here Batman is routinely defeating gods and ur-gods by holding to these values.
Inbetween we get Batman: Gothic, where reason and rationality are shown to be effective but limited. Batman solves the mystery, but an epilogue reveals that he's been blind to a major player in the events....the Devil himself! Humanism works here, but remains oblivious to the man behind the curtain.
The Devil next reappears in Morrison's Batman mythos during RIP, where he's wearing Mangrove Pierce's body and using the name 'The Black Glove'.
Batman is invested in a project which attempts to improve humanity through reason and rationality. There's no greater threat to that than the possibility that deep down inside humanity is a kind of irrational evil from which it can never escape.
The Devil's the ultimate supernatural bogeyman. There's no greater threat to it than the possibility that people might one day be able to work and think their way free. If that's true then the Devil's days are numbered.
The Joker is well aware of who the Black Glove is, making numerological references to the Devil, quoting the Rolling Stones and illustrating the point by fashioning himself a serpent's tougue. He also claims to know why the Devil hates Batman (#680) and it has to be because of this; the possibilities for humanity that Batman's values and achievements represent scare the Devil (#681).
Batman has to acknowledge though that the Devil is a part of him. Just as humanism tried to exclude from its discourse the irrational side of human experience, Batman tried to fence off the nonsensical aspects of his own life experience inside The Black Casebook; "All the things we'd seen that didn't fit and couldn't be explained went into the Black Casebook" (#665) but when he writes the final entry in the Casebook he faces the posibility that he's reached the limits of reason.
In the various isolation experiments, initiations and Thogal rituals we've seen Batman undertake he's found this 'source of pure evil' deep down inside himself. And as Doctor Hurt breathes, "The Black Glove always wins" it is Batman's own black glove we see smashing through the helicopter window.
Since we're talking about a book set in the shared universe of the DCU we have to mention that this is a world not short of Devils and Devil-analogues... Neron, Satanus, the First of the Fallen, Lucifer and plenty of others could all in different ways be thought of as 'The Devil' in DCU continuity.
I would suggest that it is not helpful in understanding Batman RIP to do so here. What Batman trimuphs against here is the idea of the Devil rather than any specific pre-existing variation on that idea. Although perhaps we should mention Orion's warning from Final Crisis #1 concerning Darkseid and his retinue of evil gods; "They did not die! He is in you all!"
It'd be tempting to give the last word to Damien, who says, "I know the Devil exists, or at least something exists which might as well be the Devil. I've met him." (Batman #666)
The Black Glove is something which might as well be the Devil.