The Twelfth Doctor + Increasing Vengeance Combo

The Twelfth Doctor on the battlefield.

Increasing Vengeance in your graveyard.

You have not cast an instant or sorcery spell from anywhere except your hand this turn.

You have an instant or sorcery card in hand.

plus enough mana to cast the instant or sorcery in your hand available

Cast the instant or sorcery spell from your hand by paying its mana cost.

Holding priority, cast Increasing Vengeance from your graveyard for its flashback cost by paying , targeting the instant or sorcery.

Increasing Vengeance's demonstrate ability triggers, causing you and an opponent to copy Increasing Vengeance, with your copy targeting the original Increasing Vengeance.

The Twelfth Doctor triggers, putting a +1/+1 counter on it.

Resolve the copy of Increasing Vengeance, copying Increasing Vengeance, with the copy targeting the original Increasing Vengeance.

Repeat from step 4.

Infinite magecraft triggers

Infinite +1/+1 counters on a creature