Pathfinder (tabletop game)/WMG

Rovagug and Tharizdun are one and the same.
Gods of wanton destruction? Check. Forced all the other gods to join forces against them? Check. Sealed away in a demiplane? Check. Rovagug and Tharizdun are aspects of the same god worshiped on Golarion and Oerth, respectively. Myths about them have diverged wildly over the ages, leading to many differences in the details, but the core story is the same. Other possible aspects include Khyber from Eberron, the wraithlike Dark God (see 2E's Monster Mythology), the oozing Elder Elemental Eye (worshiped in Greyhawk), and the Drow god Ghaunadaur.
 * The Elder Elemental Eye is explicitly a hidden avatar of Tharizdun, so very possibly.

Aroden knew his death was coming.
Aroden had fostered two goddesses risen from mortal humanity, Aranzi and Iomedae, because he knew he would need a successor. Either something was coming for him, or some inevitable threat was on its way that would require a Heroic Sacrifice from Aroden, the last Azlanti on the planet, himself.
 * Something tells me that Aroden's death (assuming he really is dead) was an effect of the strange occurences across Golarion, not the cause. To my knowledge, Aroden was only worshiped in Avistan and northern Garund, but the fallout was felt worldwide.

What Zon-Kuthon did to his father wasn't malicious.
We know that ZK still feels in his way some of the attachments he had during his days as Dou-Bral (see: Shelyn), and that he has a severely warped sense of what is and is not desirable. Maybe he just wanted a little Nightmare Fetishist father/son bonding?

That unspecified otherworldly wrongness that turned Dou-Bral into Zon-Kuthon? The internet.
To be specific, direct psychic contact with the more disturbed and disturbing corners of it. Encountering either some of the weirder manifestations of the Furry Fandom or absorbing the psychic energy of the Furry Hatedom is probably to blame for his attack on his dad. (Who, remember, was a wolf-spirit.)

Lamashtu's influence has reached Earth, and Lady Gaga is her herald.
Lamashtu is the three-eyed Mother of Monsters and associated with childbirth and fertility. "Born This Way" is "the manifesto of Mother Monster", features lots of weird birthing imagery, and shows Gaga with an extra eye in the opening monologue. Consider also that Lamashtu is the goddess of madness and nightmares, and Gaga's videos are known for their generous doses of creepiness and WTFery.

The SCP Foundation has at least one minor Spawn of Rovagug in custody.
682, clearly some kin to the Tarrasque, is the obvious one.

Imrijka is actually a Jägermonster.
She definitly would not look out of place if depicted in Girl Genius: She has green skin and fangs and wears clothes that fit perfectly, most importantly the hat. She probably was somehow teleported to Golarion- which could be both thanks to a Spark's experiment or due to conjuration, and has false memories according to which she is a half-orc.

Aroden fell into a black hole.
That's why his death couldn't be foretold: because the "no information can escape" rule applies to metaphysical information being flung backwards in time (the raw material of prophecy) as well as mundane stuff. (Not to mention all the temporal weirdness inherent in black holes and such.)

Alchemists' Sunlight Bombs are tiny hydrogen bombs.
I suppose it's more likely that they just include some kind of flash powder that gives off ultraviolet light as it burns, but - Rule of Cool.