Basically the shell of how I would build a -1/-1 tokens deck in this format. It is slow, and depending on how aggressive your meta is and how much you are willing to spend I would mix in some control spells as you see fit. Should be able to grind out any slower creature based decks and play enough cheap big things to storm over most everything else.

Nest of Scarabs, Obelisk Spider and Consuming Fervor will be your three cornerstones to winning a match. Between the token generation, card draw and mana ramp, you should be able to flood the board wide and tall. Ammit Eternal is another strong early game threat that synergises incredibly well with Consuming Fervor .

Main Interactions

A lot of draining occurs when Obelisk Spider is on the field, as well as Snake tokens from Hapatra, Vizier of Poisons:

Upkeep: Consuming Fervor drains the enemy and creates tokens. Best placed on Exemplar of Strength. Channeler Initiate or Ammit Eternal so they can manage the counters, otherwise combat tricks will have to manage.

Declare Attackers: Decimator Beetle drops another counter on an enemy as well taking one off your team. These occur separate of one another; you do not need to remove a counter from your side to drop one on the enemy. Redundant as the Beetle has been dropped.

Combat Damage Step: Hapatra, Vizier of Poisons and Obelisk Spider trigger at this point.

Thats without looking at any ETB or sorcery speed counters, including The Scorpion God , which all should resolve at a separate time and thus generating tokens and pinging the enemy separately. Combat tricks would be best played during Blockers Declaration to ensure they trigger more pings and tokens.

Notes

Multiple -1/-1 counters resolving at the same time will only generate one snake token and one drain effect, but will generate multiple scarabs.

Dropping ETB counters onto scarabs will kill them and generate more scarabs. I believe more than one Nest of Scarabs on the field will multiply the number of scarabs generated in this manner. Example, dropping Exemplar of Strength's tokens onto a scarab with two Nests out will kill one scarab and generate six more in its place.

The Scorpion God should hopefully be drawing you cards constantly, as the aim of the deck is to have -1/-1 counters all over the place. While piling multiple -1/-1 counters on one scarab will make you go wide very fast, dropping them on multiple scarabs will generate you a lot of card draw.

Consuming Fervor on an Exemplar of Strength will generate you 1 Snake, 1 Scarab and 2 Health a turn, so long as you keep swinging with the Exemplar, all on a 7/7 body for 3 mana. With the proper setup of course.

Key to the City super strong synergy between Hapatra, Vizier of Poisons and Ammit Eternal. Unsure what to replace to fit it into the main deck though, any further suggestions on this point would be appreciated.

2x Cascading Cataracts to ensure mana fixing even if Chaneller Initiate's are getting picked off to allow for Grind / Dust. Its just too powerful a set of removal to not have access to it.

Maybeboard

Still on the fence between Decimator Beetle and Ammit Eternal. Ammit is a lot more aggressive and better costed, but needs to actually apply combat damage to drop counters from itself, while Beetle applies and removes counters during attacker declaration. Ammit has some other interesting interactions that Ive listed below.

Going towards green, Majestic Myriarch will go very tall with all the tokens being produced, while Overcome will allow you to storm over your opponent. Also, just one Majestic Myriarch will activate Rhonas the Indomitable as the Chimera counts itself and will be a 4/4 with indestructible and deathtouch. Destined / Lead can be used at this point to clear the enemy's board. Crocodile of the Crossing must be mentioned because its been suggested too much to ignore. Not the biggest fan but if this many people praise it perhaps its me who isnt seeing its strength. Shed Weakness looks meh now that Ive noticed it only removes one -1/-1 counter. Heroic Intervention looks like it would fit well as well, as does Blossoming Defense.

Going towards red, Soul-Scar Mage will turn Magma Spray, Abrade and even Electrify into more token generators, as well as making them very effective shrinkers against targets they wouldnt be able to kill normally. Sweltering Suns could be considered for board wipes, with every scarab burnt this way generating three more, let alone every other creature. Blur of Blades is pretty meh, Id only consider it going even further towards a budget deck.

Going towards black, Doomfall can help you disrupt the enemy's plans and see how aggressive they will be. Lethal Sting is amazing removal with multiple interactions. If you can afford it, I would include Fatal Push as this is more of a slow deck and would be best complemented with early control. Ammit Eternal will also start to punish enemy spell casters as it will ping them and generate tokens on every cast, but keep a combat trick ready to cleanse it. Banewhip Punisher is just OK removal, though Stinging Shot does almost the same thing for cheaper, and Festering Mummy is just a useful tool to ping the enemy and dump counters on early.

Driven / Despair with a large amount of tokens will possible discard your opponents hand and fill your own.

With enough -1/-1 counters on enemy creatures, Grind / Dust threatens to be amazing removal. Will need mana fixing on the field though.

Further mana ramp and fixing with Naga Vitalist and Manalith , absolutely not sure where these would fit and would likely weaken the deck overall.

Westvale Abbey defeats the purpose of this being a rotation proof deck and being budget, but will add yet another powerful threat that can consume a bunch of beetles very quickly.

Crested Sunmare would be insanely hard to play, but with all the life gain going on in this deck between Exemplar of Strength and Obelisk Spider I couldnt help but add it to the list. It would be pretty fun to see it get going.

Example Turn Sequence

Turn 1: Dual Land

Turn 2: Channeler Initiate

Turn 3: Ammit Eternal, Consuming Fervor

or

Turn 1: Dual Land

Turn 2: Hapatra, Vizier of Poisons

Turn 3: Nest of Scarabs

Turn 4: Channeler Initiate, Exemplar of Strength, 6 Scarabs, 2 Snakes

or

Turn 1: Dual Land

Turn 2: Exemplar of Strength

Turn 3: Consuming Fervor , Hapatra's Mark, Dual Land

Ending Thoughts

Where I think this deck is weakest is the lack of creatures to drop at 1 mana, as nothing seemed to be worth taking out for any 1 drop, as well as an awkward gap around the 4 mana drop, especially noticeable if you drop a Channeler Initiate at turn two. It is also has very low interactivity outside the sideboard. Finally, I am terrible with organising a landbase, but since this deck is already slow the dual lands in this set entering untapped doesnt seem like a big deal, especially if you draw them late game and need to cycle them out.

Edits

Edit 1: Removed 4x Shed Weakness 1x The Scorpion God 1x Nest of Scarabs, Added 3x Grind / Dust 3x Driven / Despair

Edit 2: Removed 3x Lethal Sting from Sideboard, Removed 2x Ifnir Dreadlands from Mainboard, Moved 3x Grind / Dust to Sideboard, Added 3x Key to the City and 2x Cascading Cataracts to Mainboard

Any and all feedback is welcome, positive or negative (though hopefully constructive). Thanks for reading.