Sedgemoor Witch triggers, creating a 1/1 Pest creature token.
Resolve Cloudshift, blinking Skullwinder.
Skullwinder enters the battlefield, returning Cloudshift from your graveyard to your hand and causing target opponent to return a card from their graveyard to their hand.
Activate Phyrexian Altar by sacrificing the Pest, adding ({W} magic symbol) .
The Pest dies, causing you to gain 1 life.
Repeat.
Results
Infinite death triggers.
Infinite ETB.
Infinite lifegain.
Infinite lifegain triggers.
Infinite LTB.
Infinite magecraft triggers.
Infinite sacrifice triggers.
Infinite storm count.
Target opponent returns all cards in their graveyard to their hand.