Win Conditions:
Hapatra/Flourishing Defenses/Nest of Scarabs + Blowfly Infestation + 2 Snakes + Zulaport Cutthroat/Poison-Tip Archer/Obelisk Spider = infinite drain

Hapatra/Flourishing Defenses/Nest of Scarabs + Ivy Lane Denizen + Cinderhaze Wretch = Everyone discards their hand + infinite snakes

Hapatra/Flourishing Defenses/Nest of Scarabs + Ivy Lane Denizen + Devoted Druid = Infinite snakes (and if IVD has haste, infinite green mana)

Devoted Druid + Quillspike = infinitely big Quillspike

Puppeteer Clique + IVD + Free sac Outlet + Zulaport Cutthroat/Poison-Tip Archer/Obelisk Spider = infinite drain and play everyone's graveyards


Potential Win Cons:
Blowfly Infestation + Kormus Bell + Urborg, Tomb of Yawgmoth = wipe all opponents lands

Archfiend of Ifnir + Generous Patron + 8 cards in hand at discard step = draw deck and board wipe
If you have Archfiend of Ifnir and Generous Patron in play, get 8 cards in hand and end your turn. You'll have to discard down to 7... which will put -1/-1 counters on all of your opponents creatures. Which will draw you a bunch of cards.
Which you then have to discard.

At some point, all your opponent's creatures will be dead, you'll have a lot of snakes on board if you had Hapatra in play, and you'll have a 7 card hand that's stacked with all of the best choices from what you drew.

References:
http://tappedout.net/mtg-decks/toxic-relationship-hapatra-edh/