Activate Phyrexian Altar by sacrificing Rendclaw Trow, adding {B/G}.
When Rendclaw Trow dies, its persist ability triggers, returning it to the battlefield from your graveyard with a -1/-1 counter on it.
Activate Quillspike by paying {B/G} and removing the -1/-1 counter from Rendclaw Trow, giving Quillspike +3/+3 until end of turn.
Repeat.

Infinite death triggers

Infinite ETB

Infinite LTB

Infinitely large Quillspike until end of turn

Infinite sacrifice triggers

Quillspike

Phyrexian Altar

Rendclaw Trow

Activate Ashnod's Altar by sacrificing Rendclaw Trow, adding {C}{C}.
When Rendclaw Trow dies, its persist ability and Necrosynthesis trigger.
Resolve the Rendclaw Trow trigger, returning it from your graveyard to the battlefield with a -1/-1 counter and a vigilance counter on it.
Resolve the Necrosynthesis trigger, putting a +1/+1 counter on Tayam.
Activate Tayam by paying {3}, removing a +1/+1 counter from Tayam, and both counters from Rendclaw Trow.
Holding priority, activate Ashnod's Altar by sacrificing Rendclaw Trow, adding {C}{C}.
Repeat steps 2-4 one additional time.
Activate Ashnod's Altar by sacrificing Rendclaw Trow, adding {C}{C}.
Resolve Tayam's ability from step 5, causing you to mill three cards and returning Rendclaw Trow from your graveyard to the battlefield.
Repeat.

Infinite +1/+1 counters on Tayam

Infinite colorless mana

Infinite self-mill

Put all permanents with a mana value of 3 or less from your library and graveyard onto the battlefield

Tayam, Luminous Enigma

Necrosynthesis

Ashnod's Altar

Activate Ashnod's Altar by sacrificing Rendclaw Trow, adding {C}{C}.
When Rendclaw Trow dies, its persist ability and Sengir's first ability trigger.
Resolve the Rendclaw Trow trigger, returning it from your graveyard to the battlefield with a -1/-1 counter and a vigilance counter on it.
Resolve the Sengir trigger, putting two +1/+1 counters on Sengir.
Activate Tayam by paying {3}, removing a +1/+1 counter from Sengir, and both counters from Rendclaw Trow.
Holding priority, activate Ashnod's Altar by sacrificing Rendclaw Trow, adding {C}{C}.
Repeat steps 2-4 one additional time.
Activate Ashnod's Altar by sacrificing Rendclaw Trow, adding {C}{C}.
Resolve Tayam's ability from step 5, causing you to mill three cards and returning Rendclaw Trow from your graveyard to the battlefield.
Repeat.

Infinite +1/+1 counters on Sengir

Sengir, the Dark Baron

Combos with "Rendclaw Trow"