A rush of colors and shapes streaked by Reaper as he fell through the mirror, struggling to restrain Grey Thorn lest he break free and disappear before wherever they were had a chance to resolve and settle.
Grey Thorn slashed at Reaper with his horn, and pawed at him attempting to dislodge his opponent's grasp, but to no avail--Reaper clung all the tighter, knowing a slip would lead to either being stranded, or consumed by the Void.
After a bit less than a minute, the sensation of falling stopped, and the swirling kaleidoscope organized into a rainbow-like pattern of muted, slowly-shifting colors, spreading out in all directions. The two combatants drifted to a stop and separated.
Reaper drew his sword and assumed a defensive stance, but Grey Thorn sat down and chewed his lower lip, looking distracted.
Reaper raised an eyebrow, sheathed his sword, and sat down nearby.
“So,” he began, cheerfully, “where are we? I assume this isn’t your first trip through that mirror.”
Grey Thorn glared back: “No. It is not. We are in a nexus of sorts, and all around you are portals to other worlds, other realities.”
Reaper looked up at the endless array of iridescent globes hovering above them.
“Alright,” he said, “so now what?”
Grey Thorn rose from the ground menacingly: “I destroy you, get my bearings, and return to my chambers to finish dealing with the two sleeping Princesses!”
Reaper nodded his acknowledgement, then shook his head: “I don’t think so. You might as well take a seat; we’re going to be here a while.”
Grey Thorn stopped, and responded uncertainly, “what do you mean? I have you at my mercy, with nopony to aid you!”
Reaper nodded again, a nod that turned into another shake of his head: “You have it backwards. You, my monstrous adversary, are at my mercy--well, mine and that thing of yours!”
He pointed at the Void, now much-diminished, hovering just behind Grey Thorn.
Grey Thorn furrowed his brow and glanced quickly over his shoulder: “What of my extension? It is a part of me--I have nothing to fear from it!”
Reaper’s face fell into a bored expression: “Look--we’re stuck together. Let’s dispense with the posturing and horseshit, please!”
He pointed again at the Void: “You know as well as I do that you don’t really control that thing--not anymore, anyway. It’s not an extension, it is, at best a symbiont.”
Grey Thorn took a step back and narrowed his eyes: “So? I have had centuries of mastery over this creation, and I--”
Reaper interrupted, “And that’s the problem: you spent centuries in Nightmare Moon’s “hothouse,” feeding that thing, growing ever more interconnected as it grew ever more ravenous. But when she changed back to Luna, and you lost your easy hunting grounds, you suddenly found that Void was too much to handle, without a new source of ever-more-energetic victims.”
Grey Thorn sat down uneasily, his eyes shifting, as though looking for an exit.
Reaper dropped into a more-comfortable, reclined position, before continuing: “You called me “Entropy’s errand-colt” as an insult, but there is some truth to it. As such, I know an imbalanced system when I see one, and you, sir, are on the wrong side of the equation!”
Grey Thorn glowered: “Then I shall just have to rebalance the equation a bit--with you!”
Reaper rolled his eyes: “Really? That’s the best you have? Surely you know I have no life energy or essence, at least not in the conventional sense.”
He unsheathed his sword: “Secondly, do you recall when I threw this at one of that thing’s tendrils, back in Appleloosa? It passed straight through. Likewise, I just phased right through the cloud or nimbus or whatever shrouds the Void itself.”
Reaper smiled: “That thing has no effect on me.”
Grey Thorn opened his mouth to object, but Reaper cut him off: “Oh, to be sure, if I jumped straight into the heart of the Void, I would likely meet the same fate as that poor, foolhardy bastard who dove in after her wingpony.”
Grey Thorn tipped his chin up proudly: “I guarantee it!”
“Granted,” Reaper concurred. “But short of that, your symbiont is no threat to me--especially outside of Equestria. It and I are both clearly bound to Equestria.”
“In fact,” he said, bringing his sword in close to trim a front hoof, “it’s a much greater threat to you!”
Grey Thorn bristled defiantly: “I will simply diminish my draw on it, so it may conserve its energy.”
“Two problems with that, G.T.,” Reaper replied, “One: that thing’s not like Tartarus’ Pit. Oh, you’ve made a pretty good model of it there, but the Pit simply is. It just sits there and exists, across all time, across all realities. It neither consumes nor emits.”
Reaper smiled sadly, and began paring his other front hoof: “Unfortunately for you, your version is more like a device or living thing. I’m sure it’s quite efficient, but Entropy always has the final word, and no equation balances perfectly. That thing must absorb energy--it’s in its nature.”
Grey Thorn licked his lips nervously.
Reaper stood up, resheathed his blade and stretched: “And don’t forget the second, similar problem--me.”
It was Grey Thorn’s turn to grin: “How? Your sword? Your magic? My unicorn magic far surpasses yours! You’re no longer in Equestria, and just as my extension is bereft of much of its power, so too are you defanged!”
Reaper nodded: “That’s true. Sort of.”
Grey Thorn looked puzzled: “You either have power, or you do not!”
“I’m not talking about power,” Reaper replied. “In much the same way as your symbiont absorbs ponies’ essences, I absorb the energy around me. If that energy is sunlight--great! If it’s the life energy of plants and insects, well, that’s OK, too, as long as I don’t stay in one place too long. But if there’s no living thing anywhere near me other than one, solitary pony, well…”
He shrugged apologetically.
Grey Thorn shot to his feet and began backing away.
Reaper walked slowly forward, keeping pace, staying just far enough away to avoid the Void: “So as I see it, you don’t really have any choice, caught as you are between a rock and a hard place, but to take us back through the correct portal at some point in time.”
“I-I don’t recall which one it is!” Grey Thorn stammered, beads of sweat forming on his forehead.
Reaper sighed: “Do you recall my earlier request regarding horseshit? Of course you know where it is! I’m sure you used that mirror many times on your various specimen-slash-sacrifice-gathering trips!”
Grey Thorn furrowed his brow: “Specimen? Sacrifice?”
“I’m Death’s agent--don’t you think I recognize non-pony remains when I see them?” Reaper replied. “I saw various bones on one of the work tables, and spied whole skeletons at the back of your creation chamber.”
He took another step forward: “That’s where we just were, isn’t it? The place you created that thing! That’s why it has the special barrier wall and no wards. That’s why the back wall is piled with victims’ remains!”
“Yes,” Grey Thorn replied, “it is the point of my maximum power, and you are unwise to wish for a return, for it would be you and me alone, and it would be over very quickly!”
“Well, not alone,” Reaper responded. “I expect Luna will be awake shortly, and rouse Twilight, then who knows what they’ll do?”
Grey Thorn bristled: “I think not! You underestimate my power! I have been observing Nightmare Moon for centuries, learning her techniques for instigating and deepening sleep, watching her craft totally-immersive dream-states!”
“Oh, I’m sure that’s true,” Reaper admitted, “and you might be able to knock Twilight out, but there’s no way the Mistress of Sleep and Dreams is falling to an amateur, no matter how talented! It’s just a matter of time.”
He looked up at the various portal-orbs, hovering above them: “Speaking of--how long have we been here? How does time pass here? Why, we might have been gone for days by now, in Equestrian terms!”
Grey Thorn shuddered violently, and the Void suddenly surged forward, causing Reaper to quickly spring sideways in order to avoid becoming ensnared.
Grey Thorn took this opportunity to jump up, off the nexus’ plain. He shot rapidly toward one of the shimmering orbs.
Reaper’s horn pulsed a deep violet, as he reached out with his magic, snagging Grey Thorn’s tail: “Oh, I don’t think so! I’m sticking to you like a burr in a mane!” His sword swept out of its scabbard reflexively.
Grey Thorn looked over his shoulder, and began firing bursts of magic at Reaper in an effort to dislodge him. Reaper parried the golden darts with his blade, while keeping a tight focus on Grey Thorn’s tail.
“We’d better hurry back, before Twilight ransacks your study, and figures out how to defeat you!” Reaper taunted, as he and Grey Thorn hurtled from orb to orb, passing briefly through reality after reality, their bodies shifting and transforming rapidly.
Reaper gritted his teeth and focused on maintaining contact with Grey Thorn at all costs. He fought to clear his mouth as they crashed through the surface an ocean for a split second, briefly gaining glittering scales and elegant fins.
Grey Thorn howled in rage as they shot out of the water, heading for the portal: “Release me!”
Reaper sputtered and spit out a mouthful of water as they reemerged over the nexus: “I’ll gladly let you go the second we pass back through the mirror on Equestria!”
“Hey!” he then shouted, in mock alarm, “What if they destroyed the mirror! What if we destroyed the mirror when I shoved us through? It did look pretty cracked and fragile!”
“No!” Grey Thorn shouted in panic, suddenly cutting hard to the right, heading for another shimmering orb. “I cannot be trapped here!”
“Well then let’s head back home and finish this, once and for all!” Reaper suggested, bracing for another portal trip, ready to release Grey Thorn the instant they hit the floor back in his lair.
“As you wish, Harbinger!” Grey Thorn spat back, bitterly, “But I do not think this will end well for you!”
They passed through the gossamer surface of the orb, and time and space bent around them wildly.
“Just as long as it ends badly for you, too!” Reaper replied grimly.