For the Disembowel + Island infinite keep in mind that spending a blue on a X=1 copy does not give us only a single Worldpurge. We should easily be able to bounce Primeval Titan, play it to return the island and bounce it again to keep in hand, ready to fetch the island after copying X=0.
To kill the reordered stage sequence I found another infinite. Sachi, Daughter of Seshiro produces green by itself without any targeting required. Just play it to get Bloodbond March triggers. For all but the last trigger return Sachi to the battlefield, get a Dual Nature token and destroy the original via legend rule. Imprint on Mimic Vat to get a hasty token that taps for green. After the last Bloodbond March trigger keep the original around, bounce it via Worldpurge and repeat.
Yeah, we need to use Worldpurge to bounce Primeval Titan every time we want to produce a blue, so we can't accumulate any. But we can produce a single blue lots of times and that should be enough to go infinite.
I'm not sure what can be done to save white creatures for after the hyperstage. We'd need a new way to ensure there are hasty token activations required to repeat the transition. That seems like a difficult problem, since bouncing all our artifacts leaves most of our board alone. Maybe we can use another effect for that part? No idea what could possibly work though.
So it's been a while since I replied and you've accumulated some ideas. Let's start with the 75 card decks.
Removing Swarm Intelligence doesn't make Disembowel safe for the island later in the sequence. Spellweaver Volute can cast a copy of Disembowel with X=0. In response to that we can do some actions to draw the actual card and cast it with X=1. Once both of the spells are on the stack we can copy the 0 version to create blue mana from the island many times (with help from Primeval Titan and Natural Affinity between the [c]Psachic Battle[/c} triggers. That blue mana can be used to copy the X=1 version to access the higher parts of the combo. Sadly this kills all the proposed decks.
Another problem with the first proposed deck is that we can repeat the megastage transition without the need for hasty Metallurgeons under the Worldpurge. Ancient Den tokens would easily produce enough mana for that. To fix that we could witch to a Walking Atlas setup. At some point we would need to create new hasty Atlas tokens under the worldpurge and those tokens are required to access the Ancient Den mana there. But that conflicts with the use of island later.
I like the use of Peak Eruption to produce red from a sorcery. You already noted the infinite with Gerrard's Verdict and multiple lands, and the fixes for that in the later versions seem to work. If it wasn't for that Disembowel problem
An idea I had for the artifact lands is to use Walking Atlas + Ancient Den + Expedition Map instead of Su-Chi + Farrelite Priest. the extra card can be saved back in the megastage transition because we would not need Primeval Titan. But we would be unable to use Gerrard's Verdict versions (the wouldn't need to cast Worldpurge) and we lose some ways to make use of lands later on, so I don't see it actually helping.
Now on to the 60 card deck. The first proposed improvement doesn't work. Restoring the Tree of Tales doesn't force us to gain the green mana right then. We can just bounce it to hand with Worldpurge and after resolving that we can put the Tree back into play as a creature, having it die but creating lots of tokens that give us the green mana on the wrong side of the transition. Going infinite.
The second version also goes infinite. This time we can repeat the hyperstage transition without need for hasty Metallurgeons in the lower stage. We can use Walking Atlas in the higher stage to put the land into play and generate the green mana. So once the ressources we have in the higher stage are running out we arrange everything as needed, resolve the Rebuild from the transition on the stack and immediatly put the next transition on the stack, getting new hasty Metallurgeon tokens via Argivian Find and Disenchant.
This infinite doesn't work in the Battle Cry version because that only gives us hasty untapped Metallurgeons if we have some tapped ones on the battlefield already. And those are destroyed by the Rebuild and we need to create new ones before we transition again, requiring Metallurgeon activations in the lower stage.
There is an infinite in the 15 stages after all. Disembowel with X=0 can destroy the animated Island. Is there any other way for goblins to produce blue?
Luckily we can do without the toughness boost for Tree of Redemption. When we want to put a new megastage on the stack we just stockpile a bunch of hasty Tree tokens. Tap the first to go to 13 life and put 4 hyperstages on the stack. Then tap the next tree, go to 13 again and put another 4 hyper stgages on the stack. continue until we run out of trees.
Yeah, opportunities for the opponent to gain life are getting low, but at least one is still there. Nectar Faerie gives lifelink to itself or some other elf/faerie. So we can donate lifelink creatures and attack into them. Opponent blocks and gains life when combat damage occurs. Allowing us to get more combats afterwards and go infinite. That particualar source of lifegain also seems near impossible to get rid of, unless we remove donations entirely.
Magus of the Candelabra untaps lands, which is not a mana ability. So it will go infinite if we try to use it as a stage creature.
Mnemonic Wall can get Disembowel to our hand, which then targets anything as soon as we get access to black mana, also going infinite. It is also an enter the battlefield effect, which we can make use of via Worldpurge without any defender targeting.
So the 15 stage sequence doesn't look too good.
The alternate 14 stage sequence seems fine. But while the stages work without donation the current layer sequence needs Pain Magnification controled by the opponent, so the saved card is lost again when we put Sky Swallower back in.
Although there is the option to try and build a layer sequence without donation. That would allow us to make use of the opponents life, and they wouldn't be able to pick discarded cards back up, providing another possible limiter.
In the presence of donation and with both players able to refill their libraries Consecrated Sphinx goes infinite, since opposing Sphinxes can keep triggering each other.
The best 75th card I can think of is a second copy of Rebuild or any other cycling card that we can't pick up without drawing it. But yeah, there is probably some better layer sequence left to find.
The Zubera can also help us get started so if we replace Finest Hour it seems we can use Five-Alarm Fire.
For the start, have Winter Blast as one of the extra cards in hand and do the typical stuff to get a good Genesis Wave going. Make sure to grab Horobi, Death's Wail and the Zubera along with some token copies. We can kill multiple Zuberas when we target them with Winter Blast. I'll not work through any numbers here, but I'm sure we can get going.
EDIT: Centaur Archer already deals damage to some of our creatures, so the less than 3 part of the damage layer sequence goes infinite.
Floating-Dream Zubera seems like a good call. But remember that we can draw Genesis Wave twice for each Zubera trigger. Once itself and once via Rebuild cycling. We can put the cycle ability on the stack as soon as we draw the card, so Rebuild is available in the graveyard and we can go through the full combo before resolving the cycling to grab Genesis Wave again. We'd get more than F_{w^3 + w14 + 2}(115) Dual Natures before combat.
Killing multiple Zuberas before resolving the first trigger allows us to draw extra cards. That seems like it should help a bit for the start.
I don't know what to do with the extra slot, but we need to rework the start anyway: Noggle Ransacker goes infinite since we can donate Su-Chi and Perpetual Timepiece allowing the opponent to pick up the discarded cards again.
Oh, Panharmonicon is a great find! We were running a bit low on fringe cases of the rules to exploit.
Interestingly we now cast multiple sorceries during the resolution of the same Spellweaver Helix ability, so we put all of their Swarm Intelligence triggers onto the stack at the same time. That means we can interweave the copies of different sorceries. For example we can go Worldpurge -> Deep Reconnaissance -> Worldpurge -> Deep Reconnaissance -> ... and move the land between battlefield and library multiple times. Luckily the land gets stuck in the graveyard when we try to include Gerrard's Verdict in the cycle, so we can't actually gain more life with that. So I haven'T found any infinites with the deck yet.
I like that the Panhamonicon also casually gets an extra layer for Goblin Bushwhackers etb ability and improves the start by getting an extra Dual Nature trigger on Copy Enchantment and Swarm Intelligence. Great results all around!
To kill the reordered stage sequence I found another infinite. Sachi, Daughter of Seshiro produces green by itself without any targeting required. Just play it to get Bloodbond March triggers. For all but the last trigger return Sachi to the battlefield, get a Dual Nature token and destroy the original via legend rule. Imprint on Mimic Vat to get a hasty token that taps for green. After the last Bloodbond March trigger keep the original around, bounce it via Worldpurge and repeat.
I'm not sure what can be done to save white creatures for after the hyperstage. We'd need a new way to ensure there are hasty token activations required to repeat the transition. That seems like a difficult problem, since bouncing all our artifacts leaves most of our board alone. Maybe we can use another effect for that part? No idea what could possibly work though.
Removing Swarm Intelligence doesn't make Disembowel safe for the island later in the sequence. Spellweaver Volute can cast a copy of Disembowel with X=0. In response to that we can do some actions to draw the actual card and cast it with X=1. Once both of the spells are on the stack we can copy the 0 version to create blue mana from the island many times (with help from Primeval Titan and Natural Affinity between the [c]Psachic Battle[/c} triggers. That blue mana can be used to copy the X=1 version to access the higher parts of the combo. Sadly this kills all the proposed decks.
Another problem with the first proposed deck is that we can repeat the megastage transition without the need for hasty Metallurgeons under the Worldpurge. Ancient Den tokens would easily produce enough mana for that. To fix that we could witch to a Walking Atlas setup. At some point we would need to create new hasty Atlas tokens under the worldpurge and those tokens are required to access the Ancient Den mana there. But that conflicts with the use of island later.
I like the use of Peak Eruption to produce red from a sorcery. You already noted the infinite with Gerrard's Verdict and multiple lands, and the fixes for that in the later versions seem to work. If it wasn't for that Disembowel problem
An idea I had for the artifact lands is to use Walking Atlas + Ancient Den + Expedition Map instead of Su-Chi + Farrelite Priest. the extra card can be saved back in the megastage transition because we would not need Primeval Titan. But we would be unable to use Gerrard's Verdict versions (the wouldn't need to cast Worldpurge) and we lose some ways to make use of lands later on, so I don't see it actually helping.
Now on to the 60 card deck. The first proposed improvement doesn't work. Restoring the Tree of Tales doesn't force us to gain the green mana right then. We can just bounce it to hand with Worldpurge and after resolving that we can put the Tree back into play as a creature, having it die but creating lots of tokens that give us the green mana on the wrong side of the transition. Going infinite.
The second version also goes infinite. This time we can repeat the hyperstage transition without need for hasty Metallurgeons in the lower stage. We can use Walking Atlas in the higher stage to put the land into play and generate the green mana. So once the ressources we have in the higher stage are running out we arrange everything as needed, resolve the Rebuild from the transition on the stack and immediatly put the next transition on the stack, getting new hasty Metallurgeon tokens via Argivian Find and Disenchant.
This infinite doesn't work in the Battle Cry version because that only gives us hasty untapped Metallurgeons if we have some tapped ones on the battlefield already. And those are destroyed by the Rebuild and we need to create new ones before we transition again, requiring Metallurgeon activations in the lower stage.
Except that Builder's Blessing lets us go infinite with Dual Nature copies of Mox Ruby, which doesn't die as a creature anymore.
Luckily we can do without the toughness boost for Tree of Redemption. When we want to put a new megastage on the stack we just stockpile a bunch of hasty Tree tokens. Tap the first to go to 13 life and put 4 hyperstages on the stack. Then tap the next tree, go to 13 again and put another 4 hyper stgages on the stack. continue until we run out of trees.
Mnemonic Wall can get Disembowel to our hand, which then targets anything as soon as we get access to black mana, also going infinite. It is also an enter the battlefield effect, which we can make use of via Worldpurge without any defender targeting.
So the 15 stage sequence doesn't look too good.
The alternate 14 stage sequence seems fine. But while the stages work without donation the current layer sequence needs Pain Magnification controled by the opponent, so the saved card is lost again when we put Sky Swallower back in.
Although there is the option to try and build a layer sequence without donation. That would allow us to make use of the opponents life, and they wouldn't be able to pick discarded cards back up, providing another possible limiter.
The best 75th card I can think of is a second copy of Rebuild or any other cycling card that we can't pick up without drawing it. But yeah, there is probably some better layer sequence left to find.
The Zubera can also help us get started so if we replace Finest Hour it seems we can use Five-Alarm Fire.
For the start, have Winter Blast as one of the extra cards in hand and do the typical stuff to get a good Genesis Wave going. Make sure to grab Horobi, Death's Wail and the Zubera along with some token copies. We can kill multiple Zuberas when we target them with Winter Blast. I'll not work through any numbers here, but I'm sure we can get going.
EDIT: Centaur Archer already deals damage to some of our creatures, so the less than 3 part of the damage layer sequence goes infinite.
Killing multiple Zuberas before resolving the first trigger allows us to draw extra cards. That seems like it should help a bit for the start.
I don't know what to do with the extra slot, but we need to rework the start anyway: Noggle Ransacker goes infinite since we can donate Su-Chi and Perpetual Timepiece allowing the opponent to pick up the discarded cards again.
Interestingly we now cast multiple sorceries during the resolution of the same Spellweaver Helix ability, so we put all of their Swarm Intelligence triggers onto the stack at the same time. That means we can interweave the copies of different sorceries. For example we can go Worldpurge -> Deep Reconnaissance -> Worldpurge -> Deep Reconnaissance -> ... and move the land between battlefield and library multiple times. Luckily the land gets stuck in the graveyard when we try to include Gerrard's Verdict in the cycle, so we can't actually gain more life with that. So I haven'T found any infinites with the deck yet.
I like that the Panhamonicon also casually gets an extra layer for Goblin Bushwhackers etb ability and improves the start by getting an extra Dual Nature trigger on Copy Enchantment and Swarm Intelligence. Great results all around!