On the end step prior to your turn, cast True Polymorph by paying {4}{U}{U}, causing Port Razer to become a copy of Eye of Vecna.
Activate The Book of Vile Darkness by tapping it and exiling it, Port Razer and Hand of Vecna, causing you to create a legendary 8/8 Vecna token that has all triggered abilities of the exiled cards.
During your next turn, deal combat damage to an opponent using Vecna.
Vecna triggers, causing you to untap each creature you control and to get an additional combat phase after this one.
Repeat from step 3.

Infinite combat damage

Infinite combat phases

Infinite mana creatures you control can produce

Infinite untap of creatures you control

The Book of Vile Darkness

Eye of Vecna

Hand of Vecna

True Polymorph

Port Razer

On the end step prior to your turn, cast True Polymorph by paying {4}{U}{U}, causing Bloodthirster to become a copy of Eye of Vecna.
Activate The Book of Vile Darkness by tapping it and exiling it, Bloodthirster and Hand of Vecna, causing you to create a legendary 8/8 Vecna token that has all triggered abilities of the exiled cards.
During your next turn, deal combat damage to an opponent using Vecna.
Vecna triggers, causing you to untap it and to get an additional combat phase after this one.
Repeat from step 3.

Bloodthirster

On the end step prior to your turn, cast True Polymorph by paying {4}{U}{U}, causing Medomai to become a copy of Eye of Vecna.
Activate The Book of Vile Darkness by tapping it and exiling it, Medomai and Hand of Vecna, causing you to create a legendary 8/8 Vecna token that has all triggered abilities of the exiled cards.
During your next turn, deal combat damage to an opponent using Vecna.
Vecna triggers, causing you to take an extra turn after this one.
Repeat from step 3 during each of your turns.

Infinite turns

Lock

Medomai the Ageless

Combos with "Eye of Vecna"