Activate Karn's first loyalty ability by putting a loyalty counter on it, causing Isochron Scepter to become an artifact creature until end of turn.
Activate creatures you control by tapping those, adding at least {3}.
Activate Isochron Scepter by paying {2} and tapping it, casting a copy of Benefactor's Draught without paying its mana cost, untapping all creatures and drawing a card.
Repeat from step 2.

Infinite card draw

Infinite draw triggers

Near-infinite storm count

Near-infinite mana creatures you control can produce

Isochron Scepter

Benefactor's Draught

Karn, the Great Creator

Activate any number of creatures you control by tapping them, adding at least {5}{G}.
Activate Isochron Scepter by paying {2} and tapping it, casting a copy of Benefactor's Draught without paying its mana cost.
Resolve Benefactor's Draught, untapping all creatures you control.
Activate Elder Druid by paying {3}{G} and tapping it, untapping Isochron Scepter.
Repeat.

Near-infinite magecraft triggers

Near-infinite untap of creatures you control

Elder Druid

Activate all mana-producing creatures you control by tapping them, adding at least {1}{G}.
Activate Charnelhoard Wurm by tapping it, dealing 1 damage to an opponent.
Charnelhoard Wurm triggers, returning Benefactor's Draught to your hand from your graveyard.
Cast Benefactor's Draught by paying {1}{G}, untapping all creatures you control and causing you to draw a card.
Repeat.
If creatures you control can tap to produce at least {2}{G}, this combo will net near-infinite mana.

Near-infinite damage

Charnelhoard Wurm

Viridian Longbow

Activate all mana-producing creatures you control by tapping them, adding at least {1}{G}.
Activate Charnelhoard Wurm by tapping it, dealing 2 damage to an opponent.
Charnelhoard Wurm triggers, returning Benefactor's Draught to your hand from your graveyard.
Cast Benefactor's Draught by paying {1}{G}, untapping all creatures you control and causing you to draw a card.
Repeat.
If creatures you control can tap to produce at least {2}{G}, this combo will net near-infinite mana.

Combos with "Benefactor's Draught"