Overview:

Counters.  Lots and lots of counters.  This deck plans to get them out and keep them growing.

Deeper Dive:

There are currently 4 types of important counters in standard:

• +1/+1 counters
• Planeswalker Loyalty counters
• Charge counters
• Lore counters

This deck wants to try to make use of most of the above.

+1/+1 Counters

Obviously, +1/+1 counters can be used to make creatures big.  Most big creatures are too easy to just chump block, but big fliers are harder to handle.  At least 1 creature must be cheap, flying, and easy to get a +1/+1 counter onto.  Merfolk Skydiver fits this description, with the added benefit of being able to also proliferate, slightly more easily than Karn's Bastion (as the required {U}{G} must be on board to have cast the skydiver).

However, there are more uses with +1/+1 counters than just growing creatures.  Trollbed Guardian and Zegana, Utopian Speaker either would allow trample to creatures with +1/+1 counters while Skatewing Spy would allow flying.  There are also cards that have additional effects when +1/+1 counters are added--with Animation Module no longer in standard, Benthic Biomancer, Growth-Chamber Guardian, and Sharktocrab with their Adapt triggers are obvious candidates.  Growth-Chamber Guardian has minimal upside (useful for at most 2 proliferates).  Benthic Biomancer has more potential, but pure card draw would be preferable.  Sharktocrab is in a perfect spot to make use of +1/+1 counters, though--sharing colors with the Merfolk Skydiver, it also removes many potential threats from play and opens up the skies for flying attacks to get through more easily.

Loyalty Counters

Very few planeswalkers care about loyalty counters beyond it being their life total and frequency at which they can use abilities (Chandra, Fire Artisan being a notable exception).  As such, planeswalkers should either have very powerful abilities that can be helpful more often, or should assist in increasing the number of counters on the board.

Ajani, Adversary of Tyrants, Ajani, the Greathearted, Jace, Arcane Strategist, Jiang Yanggu, Wildcrafter, Nissa, Who Shakes the World, and Vivien of the Arkbow all add counters to the board.  Of these, both Ajani's and Jace have significant additional benefit.  By the time a 6 CMC Jace, Arcane Strategist can land on the board, it is likely to add less benefit than the mana would otherwise be used for (more proliferation), but both Ajanis fit the needs of the deck well (although the 2{W} cost of Ajani, Adversary of Tyrants may be too high).

On the other side, Kaya, Bane of the Dead, The Wanderer, Ugin, the Ineffable all have strong removal as their minus abilities, while Tamiyo, Collector of Tales simply has a powerful minus and Teferi, Hero of Dominaria would benefit from getting to ultimate more quickly.  However, none of these cards appear to improve the deck more than any cards they would replace.

Charge Counters

There are a few artifacts that use charge counters in the current standard rotation.  Transomgrifying Wand is significantly better if it's able to gain additional charges, and Primal Amulet // Primal Wellspring would be able to transform more quickly, but given sufficient proliferation Magistrate's Scepter has the potential of yielding infinite turns.

Lore Counter

There are three Sagas thatwork toward the goal of a large number of counters: Song of Freyalise, Triumph of Gerrard, and Phyrexian Scriptures.  Of these, Song of Freyalise is the one that most fits into the deck, but it itself gains little meaningful benefit from proliferation.  Generally a card slot taken by it would be better served by a Courage in Crisis.

Important to note however, it is possible to add lore counters to opponent's Sagas, preventing them from getting full benefit of their spells.  For example, ticking a History of Benalia up to a 3rd lore counter as the result of combat would give the opponent's knights +2/+1 after combat on your turn--not very useful for them!

Proliferation

Beyond getting counters onto the board, there need to be ways to proliferate them.  Evolution Sage and Karn's Bastion help remove the sting of flooding while Merfolk Skydiver, Polenbright Druid and Courage in Crisis all both allow adding counters in addition to allowing proliferation of counters.

Play Tips:

The ideal starting hand includes a Grateful Apparition, either a Pollenbright Druid or a Merfolk Skydiver, and the land to get both out.  An ideal first few turns would look something like:

Turn 1: Land

Turn 2: Land, Grateful Apparition

Turn 3: Land, Pollenbright Druid (with +1/+1), attack and proliferate Druid (to a 3/3)

Turn 4: Land, either Sharktocrab or Ajani, the Greathearted (using his -2), attacking to proliferate.

Beyond the first few turns, the goal would be to keep the opponent's threats at bay while attacking in the air.  Ajani, the Greathearted's vigilance helps with both of these goals.

Card Tips:

Grateful Apparition

Frequently one of the key cards in this deck, it is tempting to put a sole +1/+1 counter on it so it will proliferate and grow larger as it attacks, or allowing it to attack through flying defenses to continue proliferating.  This is almost always a mistake--it makes the card a bigger threat and more likely to be removed.  Having an Ajani, Adversary of Tyrants out to bring it back if removed does make putting counters here an easier choice.

Sharktocrab

2{U}{G} is an expensive +1/+1 counter.  It may make sense to put the counter on this card from another source, both to get an opponent's creature tapped cheaply, and to enable proliferation more quickly.

Magistrate's Scepter

Using the Magistrate's Scepter is difficult--seldom is it good to get out turn 3 for a turn 4 activation.  Getting out and activating when there are 7 lands on the table is better, especially if a profilerate (or two) can occur that turn.  It's also important to not take the free turn at 3 counters unless it either guarantees a win or prevents a guaranteed loss.  Much better to get to 4 to keep the 1 counter to proliferate off of.

Shapers of Nature

This both is a way to get +1/+1 counters onto the board (and to add to Sharktocrab if a flier needs to be taken out of the picture for the Grateful Apparition to get through), but also is the card draw for the deck.

Other Cards:

Some cards feel like they fit, but didn't make the cut:

Simic Ascendency -- Proliferating reduces the number of +1/+1 counters needed, but this card is unlikely to win the game when it otherwise would have been a loss.

Blast Zone -- Potentially good for taking out some tiny or huge threats, but there are too many 2-4CMC cards this deck wants to keep around.  And Karn's Bastion already has colorless mana, more is going to make it hard to get key cards out early.

Check Lands -- More check lands might reduce the cost necessary to get key cards out, however they also add more potential to not be able to get the needed land usable at all at the required time.  Instead, a full set of shock lands is preferred, as it's worth the life to be more certain to get cards played when needed.