Proliferate

[Borg]

This deck is built around two nearly identical creatures : Thrummingbird and Grateful Apparition
The deck wants to leverage their Proliferate ability to turn them into SuperLords for creatures and provide a steady increase of Loyalty for Planeswalkers and Fade counters for Enchantments.

Three creatures have superb synergy with them and form the core of the deck.

Walking Ballista
The more Proliferate effects, the stronger he gets.
Board control and beatdown in one creature.
(Eyeing the Ragavans of this world)

Stonecoil Serpent
A T1 drop who can grow with Proliferate or a late drop for an immediate 4/4 or more.
Reach comes in handy vs DRC/Delver/Murktide

The creature that possibly pushes the deck over the top however is Luminarch Aspirant.
A T1 Serpent, followed by a T2 Aspirant is a nice opening.
Ballista + Aspirant is also a great combination to have in play but what makes them really so good imo is that they can put a counter on Thrummingbird or Grateful Apparition who both from that moment on can benefit from their own Proliferate ability as well and grow bigger with every hit.

The deck has a few other usual suspects of course.

Parallax Tide
Remove opponent's lands and never look back with the help of a steady addition of Fade counters.
Once you got one of these in play, you should be able to take over the game, depending on how mana greedy the opponent's deck is.

Teferi, Time Raveler
The deck's answer against troublesome artifacts and enchantments.
With one or more Loyalty counters added every turn, you can probably bounce/draw every two turns at least.

Jace, the Mind Sculptor
With just 1 Proliferate effect per turn he can bounce a creature every turn and never run out of Loyalty.
Once a Tide is in place, the opponent may not even have the mana available to recast the creature.

Put all this in a FoW, Brainstorm, Ponder, Daze shell and you get ...

//CC0 - 7
4 Stonecoil Serpent
3 Walking Ballista

//CC1 - 10
4 Ponder
4 Brainstorm
2 Swords to Plowshares

//CC2 - 14
4 Thrummingbird
4 Luminarch Aspirant
4 Grateful Apparition
2 Daze

//CC3 - 1
1 Teferi, Time Raveler

//CC4 - 4
3 Parallax Tide
1 Jace, the Mind Sculptor

//CC5 - 4
4 Force of Will

//Lands - 20
4 Tundra
4 Island
4 Flooded Strand
2 Calciform Pools
1 Windswept Heath
1 Scalding Tarn
1 Polluted Delta
1 Plains
1 Misty Rainforest
1 Marsh Flats

//Sideboard 8 so far
2 Parallax Wave
2 Narset, Parter of Veils
1 Walking Ballista
1 Teferi, Time Raveler
1 Swords to Plowshares
1 Parallax Tide

[FTW]

Proliferating the Parallax enchantments seem fun, but then you need mana acceleration because they're too slow on 4 lands. Daze also looks bad for the same reason.

Calciform Pools is also too slow. Instead you could proliferate Saprazzan Skerry/Remote Farm to have lands that permanently tap for UU or WW. Then you can play your threats faster and also go up to 4 Ballista.

Mikaeus, the Lunarch seems better than Luminarch Aspirant because you can buff all your creatures at once, then proliferate all of them and Mikaeus. Luminarch Aspirant has better tempo though (put a counter on Apparition before combat, attack and proliferate itself immediately).

Hangarback Walker seems good.

Skyship Plunderer has a similar effect but not as good as Thrummingbird and Grateful Apparition.

[Borg]

Yes, the deck is still too slow.
I've had the parallax cards since they were released and have always wanted to make a - competitive - deck with them.
I'm still working on it more than 20 years later :)

Saprazzan Skerry : the etb tapped is too much of a handicap imo.

Mikaeus works wide while Aspirant works deep.
Mikaeus can put 1 counter at most on a creature each turn, while multiple Aspirants can put multiple counters on 1 creature ( even themselves ).
Aspirants are better on their own while Mikaeus needs - as much as possible - other creatures to be most effective.

It's still a work in progress though.
Maybe the deck has to use Ancient Tomb for the quick start like for example
T1 Ballista
T2 Bird/Spirit
T3 Tide