How can you create a combo with Gnawing Vermin, Underworld Breach, Phyrexian Altar, Yarok, the Desecrated?
user
[START OF COMBO]This combo can be formed with Gnawing Vermin, Underworld Breach, Phyrexian Altar, Yarok, the Desecrated

Color identity: UBRG
Mana cost: 
Steps:
  1. Activate Phyrexian Altar by sacrificing Gnawing Vermin, adding {B}.
  2. Gnawing Vermin dies, triggering its second ability, causing target creature you don't control to get -1/-1 until end of turn.
  3. Cast Gnawing Vermin from your graveyard for its escape cost by paying {B} and exiling three other cards from your graveyard.
  4. Gnawing Vermin enters the battlefield, triggering its first ability twice, causing you to mill four cards.
  5. Repeat.[END OF COMBO STEPS]

Result:
  - Infinite self-mill
  - Near-infinite death triggers
  - Near-infinite enters the battlefield
  - Near-infinite leaves the battlefield
  - Near-infinite mill
  - Near-infinite sacrifice triggers
  - Near-infinite storm count[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - All permanants must be on the battlefield
  - You have at least three cards in your graveyard.
[END OF COMBO PREREQUISITES]
assistant