Attempt to draw card, instead choosing to mill 6 cards and return Golgari Grave-Troll 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 Golgari Grave-Troll.
Repeat.

Infinite self-mill

Benthic Biomancer

The Wise Mothman

Golgari Grave-Troll

Activate Golgari Grave-Troll's cycling ability by paying {0} and discarding it, causing you to mill a number of cards and return Golgari Grave-Troll 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 six cards and return Golgari Grave-Troll from your graveyard to your hand, and then causing you to discard Golgari Grave-Troll.
Thran Vigil triggers, putting a +1/+1 counter on Benthic Biomancer.
Repeat from step 2.

Combos with "Golgari Grave-Troll"