Cast Channel by paying {G}{G}.
Activate Phyrexian Altar by sacrificing Skemfar Shadowsage, adding {U}.
When Skemfar Shadowsage dies, Fool's Demise's first and second abilities trigger.
Resolve the first Fool's Demise trigger, returning Skemfar Shadowsage from your graveyard to the battlefield.
When Skemfar Shadowsage enters the battlefield, it triggers, causing you to gain at least 4 life.
Resolve the second Fool's Demise trigger, returning it from your graveyard to your hand.
Activate Channel four times by paying 4 life, adding {C}{C}{C}{C}.
Cast Fool's Demise by paying {4}{U}, attaching it to Skemfar Shadowsage.
Repeat from step 2.
If you control five or more creatures that share a creature type, this combo nets infinite lifegain and colorless mana.

Infinite colorless mana

Infinite death triggers

Infinite ETB

Infinite lifegain

Infinite lifegain triggers

Infinite LTB

Infinite sacrifice triggers

Infinite storm count

Fool's Demise

Channel

Phyrexian Altar

Skemfar Shadowsage

Combos with "Skemfar Shadowsage"