Preston, the Vanisher, Delney, Streetwise Lookout, Sefris of the Hidden Ways, and Barrowin of Clan Undurr Combo

Preston, the Vanisher, Delney, Streetwise Lookout, Sefris of the Hidden Ways, and Barrowin of Clan Undurr

Here's how the cards Preston, the Vanisher, Delney, Streetwise Lookout, Sefris of the Hidden Ways, and Barrowin of Clan Undurr results in Cast a subset of spells in your library, Near-infinite +1/+1 counters, Near-infinite ETB, Near-infinite LTB, Near-infinite Treasure tokens, Near-infinite card draw, Near-infinite colored mana, Near-infinite creature tokens, Near-infinite death triggers, Near-infinite draw triggers, Near-infinite lifegain, Near-infinite lifegain triggers, Near-infinite lifeloss, Near-infinite lifeloss for all players, Near-infinite sacrifice triggers, Near-infinite ventures into the dungeon, and Return most creature cards from your graveyard onto the battlefield

Preston, the Vanisher

Delney, Streetwise Lookout

Sefris of the Hidden Ways

Barrowin of Clan Undurr

Prerequisites

Preston, the Vanisher on the battlefield
Delney, Streetwise Lookout on the battlefield
Sefris of the Hidden Ways on the battlefield
Barrowin of Clan Undurr in the graveyard

Steps

Complete a dungeon
Sefris' second ability triggers twice due to Delney
Resolve the first trigger, returning up to one other creature from your graveyard to the battlefield
Resolve the second trigger, returning Barrowin of Clan Undurr from your graveyard onto the battlefield
When Barrowin of Clan Undurr enters, it triggers once and Preston triggers twice due to Delney
Resolve a Preston trigger, creating a token copy of Barrowin of Clan Undurr that is a 0/1 Illusion
When the Barrowin of Clan Undurr token enters, it triggers twice due to Delney
Resolve the first Barrowin of Clan Undurr token trigger, venturing into Tomb of Annihilation and into the Trapped Entry room, causing each player to lose 1 life
Resolve the second Barrowin of Clan Undurr token trigger, venturing into the Oubliette room, causing you to discard a card and then sacrifice the nontoken Barrowin of Clan Undurr
Resolve the second Preston trigger from step 5, creating a token copy of Barrowin of Clan Undurr that is a 0/1 Illusion
When the Barrowin of Clan Undurr token enters, it triggers twice due to Delney
Resolve the first Barrowin of Clan Undurr token trigger, venturing into the Cradle of the Death God room, creating a 4/4 legendary The Atropal creature token and completing Tomb of Annihilation
If you control two or more The Atropal tokens, put all but one into your graveyard due to the legend rule
Repeat from step 2