Cast Mourning by paying 2 life if able, or otherwise.
Each creature you control's extort ability triggers.
Resolve the first extort trigger, causing you to pay 2 life if able, or W/B otherwise, causing each opponent to lose 1 life and you to gain that much life.
Repeat step 3 for each remaining extort trigger.
Resolve Mourning, attaching it to a creature you control.
Activate Mourning by paying 2 life, returning it from the battlefield to your hand.
Repeat until an opponent loses the game due to having 0 or less life.
This clever loop turns a humble Aura into a lethal weapon by capitalizing on cost-reduction and life-as-mana substitution. K'rrik, Son of Yawgmoth does the heavy lifting by letting you pay life instead of black mana, allowing you to repeatedly cast Mourning and activate its bounce ability for just life. Meanwhile, Pontiff of Blight grants every creature you control extort, which triggers off every single one of those castings to drain your opponents and pad your life total. To make the math work smoothly, Artist's Talent reduces the cost of your noncreature spells so that Mourning can be recast indefinitely, turning a trickle of life into a torrent of near-infinite lifeloss.