You have a black nonartifact permanent card in hand with mana cost ({B} magic symbol) .
You control a nontoken nonartifact black permanent with mana cost ({B} magic symbol) that shares a card type with the card in hand.
Steps
Cast the black permanent card in your hand by paying 2 life.
Defiler of Flesh and Aetherflux Reservoir triggers.
Resolve the Defiler of Flesh trigger, giving target creature +1/+1 and menace until end of turn.
Resolve the Aetherflux Reservoir trigger, causing you to gain 1 life for each spell you've cast before it this turn.
The black permanent enters the battlefield, triggering Cloudstone Curio, returning another nontoken nonartifact black permanent with mana cost ({B} magic symbol) from the battlefield to your hand.
Repeat.
Once you have infinite life, you may activate Aetherflux Reservoir infinite times to deal infinite damage to any target(s).