Chainer, Dementia Master + K'rrik, Son of Yawgmoth + Gray Merchant of Asphodel + Altar of Dementia

Chainer, Dementia Master
K'rrik, Son of Yawgmoth
Gray Merchant of Asphodel
Altar of Dementia

Requires
All permanents on the battlefield. Your life total is at least ten. Your devotion to black is at least ten or you have at least two opponents.
Steps
  1. Activate Altar of Dementia by sacrificing Gray Merchant, causing target player to mill cards equal to Gray Merchant's power
  2. Activate Chainer by paying nine life, returning Gray Merchant from your graveyard to the battlefield as a Nightmare in addition to its other creature types
  3. Gray Merchant enters the battlefield, causing each opponent to lose life equal to your devotion to black and causing you to gain life equal to the amount of life lost this way
  4. Repeat
Results
Infinite ETB. Infinite LTB. Infinite death triggers. Infinite sacrifice triggers. Infinite lifegain. Infinite lifegain triggers. Infinite lifeloss. Infinite mill. Infinite self-mill. Put all creature cards from all graveyards onto the battlefield under your control.