Attempt to draw card, instead choosing to mill 5 cards and return Stinkweed Imp from your graveyard to your hand.
If you milled a nonland card, The Wise Mothman triggers, putting a +1/+1 counter on Benthic Biomancer.
Benthic Biomancer triggers, causing you to draw a card and discard Stinkweed Imp.
Repeat.

Infinite self-mill

Benthic Biomancer

The Wise Mothman

Stinkweed Imp

Activate Stinkweed Imp's cycling ability by paying {0} and discarding it, causing you to mill a number of cards and return Stinkweed Imp from your graveyard to your hand due to its dredge ability.
Repeat.

Rhet-Tomb Mystic

New Perspectives

Put a +1/+1 counter on Benthic Biomancer.
Benthic Biomancer triggers, causing you to mill five cards and return Stinkweed Imp from your graveyard to your hand, and then causing you to discard Stinkweed Imp.
Thran Vigil triggers, putting a +1/+1 counter on Benthic Biomancer.
Repeat from step 2.

Thran Vigil

Cast Stinkweed Imp by paying {B} due to The Sibsig Ceremony.
When Stinkweed Imp enters, The Sibsig Ceremony and The Great Henge trigger.
Holding priority, activate Phyrexian Altar by sacrificing Stinkweed Imp, adding {B}.
Resolve the Sibsig Ceremony trigger, failing to destroy Stinkweed Imp as it's no longer on the battlefield and creating a 2/2 Zombie Druid creature token.
Resolve the The Great Henge trigger, causing you to mill five cards and return Stinkweed Imp from your graveyard to your hand due to Stinkweed Imp's dredge ability.
Repeat.

Near-infinite creature ETB

Near-infinite storm count

Near-infinite creature LTB

Near-infinite death triggers

Near-infinite creature sacrifice triggers

Near-infinite colored mana

Near-infinite creature tokens

The Sibsig Ceremony

Phyrexian Altar

The Great Henge

Attempt to draw a card. 
The draw will be replaced by Chains of Mephistopheles, instead causing you to discard Stinkweed Imp. Then, the draw will be replaced by Stinkweed Imp's dredge ability, causing you to mill cards and return Stinkweed Imp from your graveyard to your hand.
Dredger's Insight's first ability triggers, causing you to gain 1 life.
Lich's Mastery triggers, attempting to draw a card.
Repeat from step 2.

Combos with "Stinkweed Imp"