Activate Xantcha for {1}, drawing a card and causing its controller to lose 2 life.
Activate Cadaverous Bloom, exiling a card from your hand and adding {B}{B} or {G}{G}.
Activate Xantcha twice using the mana generated, drawing 2 cards and losing Xantcha's controller 4 life.
Activate Cadaverous Bloom exiling a card from your hand adding {B}{B} or {G}{G}.
Repeat from step 3.
If the player controlling Xantcha reaches a point where they only have 1 or 2 life remaining, you may hold priority and activate her any number of times before the player dies and she is exiled to draw as many of the remaining cards in your library as you wish.

Infinite draw triggers

Near-infinite black mana

Near-infinite card draw

Near-infinite green mana

Near-infinite lifeloss for target opponent

Cadaverous Bloom

Zirda, the Dawnwaker

Xantcha, Sleeper Agent

Activate Grim Monolith's first ability by tapping it, adding {C}{C}{C}.
Activate Xantcha by paying {3}, causing its controller to lose 2 life and you to draw a card.
Activate Mind over Matter by discarding a card, untapping Grim Monolith.
Repeat.

Infinite lifeloss for target opponent

Infinite looting

Infinite self-discard triggers

Mind Over Matter

Grim Monolith

Activate Thran Dynamo by tapping it, adding {C}{C}{C}.
Activate Xantcha by paying {3}, causing its controller to lose 2 life and you to draw a card.
Activate Mind over Matter by discarding a card, untapping Thran Dynamo.
Repeat.

Thran Dynamo

Activate Basalt Monolith's first ability by tapping it, adding {C}{C}{C}.
Activate Xantcha by paying {3}, causing its controller to lose 2 life and you to draw a card.
Activate Mind over Matter by discarding a card, untapping Basalt Monolith.
Repeat.

Combos with "Xantcha, Sleeper Agent"