Hapatra, Vizier of Poisons (Golgari Combo) (EDH / Commander)

Strategy
Early game we want to play Hapatra, Vizier of Poisons as quickly as possible and look to start spawning snakes with her ability. There are 5 cards allowing a turn 1 Hapatra, Vizier of Poisons. They are Gemstone Caverns, Chrome Mox, Lotus Petal, Jeweled Lotus and Elvish Spirit Guide. Other viable starting hands would be a mana dork or ramp spell into strong plays on turn 2-3 (Demonic Tutor, Earthcraft, Yawgmoth, Thran Physician). In this case we are giving up the kill threat on opponents dorks in exchange for accelerating our own game plan, and Hapatra can be played once we are ready to take advantage of her second ability.

Mana accelerants like Earthcraft (+ basic lands) turn snakes into efficient mana dorks. These let us spring ahead of our opponents as we can produce mana and create chain reactions of using our mana to spawn snakes with some spell, which then in turn provide us more mana to cast more.
Strong mana sources like Gaea's Cradle give us lots of mana after we have snakes down.

Card advantage can be obtained reliably from Skullclamp and Yawgmoth, Thran Physician. We can get cards through combat with Toski, Bearer of Secrets.

Depending on the game state, we can either look to go wide for a Craterhoof Behemoth / Triumph of the Hordes (or even Fynn, the Fangbearer) victory or assemble one of the handful of combos.

Combos
Yawgmoth, Thran Physician + Hapatra, Vizier of Poisons + (Ivy Lane Denizen / Young Wolf / Butcher Ghoul / Strangleroot Gheist) + (Blood Artist / Zulaport Cutthroat / Obelisk Spider / Poison-Tip Archer)

• Activate Yawgmoth by sacrificing one of our snakes to place a -1/-1 counter on a valid target and draw a card. This will trigger Hapatra to make a new token to replace the sacrificed creature. With Ivy Lane Denizen placing +1/+1 counters to cancel out the -1/-1 we place each iteration we have an inifinite outlet for -1/-1 counters which means we can activate Yawgmoth until we run out of life or cards. An undying dork also will work as an infinite outlet for -1/-1 counters as long as we have access to our graveyard.
• With this combo, having the drain piece down initially is not always necessary since we can draw until we find it
• Playing Blood Artist, Zulaport Cutthroat or Obelisk Spider will negate the life loss from Yawgmoth's ability
• If we have Earthcraft and a basic Forest down, we can cast Green Sun's Zenith for X=0 with the mana from each new snake in order to create an infinite library to draw from if we would run out of cards before killing the table

Mikaeus, The Unhallowed + Devoted Druid + (Blood Artist / Zulaport Cutthroat / Obelisk Spider / Poison-Tip Archer)

• Activate Devoted Druid to untap it and place a -1/-1 counter on it, this will either kill it triggering Mikaeous to return it to the battlefield with a +1/+1 counter from undying, or it will remove the +1/+1 counter on it. Repeat for infinite death triggers to drain the table.
• Without a drain source to win with, this will alternatively make infinite tokens with Hapatra, Vizier of Poisons and infinite mana with Earthcraft and basic lands and kill with Concordant Crossroads to give them haste

Yawgmoth, Thran Physician + (Young Wolf / Butcher Ghoul / Strangleroot Gheist) + (Young Wolf / Butcher Ghoul / Strangleroot Gheist) + (Blood Artist / Zulaport Cutthroat / Obelisk Spider / Poison-Tip Archer)

• Activate Yawgmoth sacrificing an undying creature WITHOUT a +1/+1 counter on it and placing a -1/-1 counter on an undying creature WITH a -1/-1 counter on it. This will cause the sacrificed creature to return with a +1/+1 counter from undying and now we repeat the process swapping which creature gets sacrificed. This results in infinite death triggers to drain the table with.
• If Earthcraft and basic lands are in play, this will give you a mana in each time a creature re-enters the battlefield before they are sacrificed.
• If Mikaeus, the Unhallowed is in play, this will work with any two non-human, non-token creatures
• Another variant on the Yawgmoth drain combo, this one not requiring the commander on board

Tutor Targets
Crop Rotation: This will normally fetch Gaea's Cradle for a huge mana boost. If that land is already in play or inaccessible for some reason, we can grab Shizo, Death's Storehouse to ensure Hapatra gets through to make snakes or a Urborg, Tomb of Yawgmoth / Yavimaya, Cradle of Growth for ramp and mana fixing options.

Demonic Tutor: An unconditional tutor which can draw us into many different strong plays. Normally, Earthcraft is the first target for mana acceleration since it is harder for us to tutor non-creatures. Yawgmoth, Thran Physician is another good first choice since he almost always will draw us a lot of cards and kill the board when we play him. Can also grab finishers like Triumph of the Hordes or Craterhoof Behemoth or a missing combo piece late game.

Diabolic Intent: Same targets as Demonic Tutor, but requires us to sac a creature first.

Vampiric Tutor: Same targets as Demonic Tutor.

Imperial Seal: Same targets as Demonic Tutor.

Chord of Calling: A creature tutor that can be quite cheap with our snakes and gets a card straight onto the battlefield. This can find Craterhoof Behemoth as a finisher if we have enough mana to dump into it, or it can find us Mikaeus, the Unhallowed for a good rate. It can of course also grab Yawgmoth, Thran Physician if we need the card draw or any of our drain pieces.

Eldritch Evolution: Some good options (sacrificing a snake token) are to grab Fynn, the Fangbearer as a finisher, Blood Artist / Zulaport Cutthroat for drain, Devoted Druid to combo off with Mikaeus, the Unhallowed, Butcher Ghoul / Strangleroot Gheist for a counter sink for Yawgmoth, Thran Physician.
Sacrificing a 1 cmc mana dork opens up the possibility of grabbing Amit Eternal to spawn a good number of snakes.
Sacrificing a 2 cmc creature gives us access to Yawgmoth, Thran Physician and Toski, Bearer of Secrets for some good card draw choices, Wickerbough Elder to hit an artifact or enchantment and Soul Snuffers for a mass -1/-1 counter effect.

Natural Order: Sacrifice a snake to put Craterhoof Behemoth on the battlefield. Can also find us Devoted Druid to combo with Mikaeus, the Unhallowed and Obelisk Spider or Poison-Tip Archer as drain pieces. This can also grab Ivy Lane Denizen to create a -1/-1 counters sink for Yawgmoth.

Green Sun's Zenith: This can be used to ramp with Dryad Arbor on turn 1. It can fetch Craterhoof Behemoth as a finisher, Devoted Druid to combo off with Mikaeus, the Unhallowed or it can fetch Obelisk Spider or Poison-Tip Archer as drain pieces. It can grab us a source of draw in Toski, Bearer of Secrets. This can also grab Ivy Lane Denizen to create a -1/-1 counters sink for Yawgmoth.