Activate Evernight Shade using Walking Ballista's second ability by removing a +1/+1 counter from it.
Repeat step 1 until Evernight Shade has no +1/+1 counters on it.
Resolve all Evernight Shade abilities dealing 1 damage to Evernight Shade, and any remaining damage to any target(s).
Evernight Shade dies as a state-based action due to having 0 toughness.
Evernight Shade's undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Repeat.

Infinite death triggers

Infinite ETB

Infinite LTB

Agatha's Soul Cauldron

Walking Ballista

Evernight Shade

Activate Evernight Shade using Triskelion's ability by removing a +1/+1 counter from it.
Repeat step 1 until Evernight Shade has no +1/+1 counters on it.
Resolve all Evernight Shade abilities dealing 1 damage to Evernight Shade, and any remaining damage to any target(s).
Evernight Shade dies as a state-based action due to having 0 toughness.
Evernight Shade's undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Repeat.

Triskelion

Activate Serrated Biskelion by tapping it, putting a -1/-1 counter on it and Evernight Shade.
Activate Phyrexian Altar by sacrificing Evernight Shade, adding one mana of any color.
When Evernight Shade dies, its undying ability and Serrated Biskelion trigger.
Resolve the Serrated Biskelion trigger, untapping it.
Resolve the Evernight Shade trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
When Evernight Shade leaves your graveyard, Thran Vigil triggers, putting a +1/+1 counter on Serrated Biskelion.
Repeat.

Infinite colored mana

Infinite lifeloss

Infinite sacrifice triggers

Serrated Biskelion

Thornbite Staff

Thran Vigil

Phyrexian Altar

Activate Serrated Biskelion by tapping it, putting a -1/-1 counter on it and Evernight Shade.
Activate Ashnod's Altar by sacrificing Evernight Shade, adding {C}{C}.
When Evernight Shade dies, its undying ability and Serrated Biskelion trigger.
Resolve the Serrated Biskelion trigger, untapping it.
Resolve the Evernight Shade trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
When Evernight Shade leaves your graveyard, Thran Vigil triggers, putting a +1/+1 counter on Serrated Biskelion.
Repeat.

Infinite colorless mana

Ashnod's Altar

Activate Champion of the Weird by paying 1 life and putting two -1/-1 counters on Evernight Shade.
Evernight Shade dies due to having 0 toughness, triggering its undying ability and Dross Harvester
Resolve the Dross Harvester trigger, causing you to gain 2 life.
Resolve the Evernight Shade trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
Resolve the Champion of the Weird ability from step 1, causing an opponent to blight 2.
Activate Champion of the Weird by paying 1 life and putting two -1/-1 counters on Evernight Shade, causing an opponent to blight 2.
Repeat.

Infinite -1/-1 counters

Infinite lifegain triggers

Champion of the Weird

Dross Harvester

Combos with "Evernight Shade"