[Pontif of Blight]
Win condition.
Mana sink, by giving every creature extort. Many cards synergies well with many (small) life gain or life loss triggers.

[Defiant Bloodlord]
Win condition, see Vizkopa Guildmage for synergies.

[Cradle of Vitality]
Get millions of counters. Almost every card in this deck enables life gain. Ordeal of Heliod will net you 10 counters.

[Cruel Sadist]
Continuous creature destruction. Enabled by feast on the fallen, Cradle of Vitality, and Serene Steward, Ordeal of Heliod. Can also give itself counters. Removal threat! Easy triggering of Ordeal of Heliod.

[Feast on the Fallen]
Enough ways to trigger loss of life, so will almost always result in 1 counter per upkeep = 2 per turn. Cards like festering wound, orhzov guildmage enable loss of life in opponents turn.

[Soul Link]
Equip on wall of souls
Example: creature deal 5 damage to wall of souls.
You deal 5 damage to the opponent and get 10 life.
Can also be put on creature an opponent controls.

[Cliffhaven vampire]
1 extra damage per extort trigger
Suture priest makes every creature you play deal 1 damage to the opponent.

[Festering Wound]
Play early. After 1 turn: 1 damage. After 3 turns 6 damage. After 5 turns 15 damage. Must be dealt with.

[Vizkopa guildmage]
3 mana for one extra damage per turn (drana's emmisary)
Mana sink: second ability can be triggered multiple times!
Ordeal of heliod trigger = 10 damage, gain 10 life. If you have 6
mana you win the game