Activate Havengul Lich by paying 1, allowing you to cast Shambling Ghast card from your graveyard this turn.
Cast Shambling Ghast from your graveyard by paying .
Activate Yahenni by sacrificing Shambling Ghast.
When Shambling Ghast dies, it triggers twice, creating two Treasure tokens.
Resolve the Yahenni ability.
Activate the Treasures by tapping and sacrificing them, adding 1
Repeat.
This loop is a masterclass in necromancy, turning Havengul Lich into a recurring engine that repeatedly plucks Shambling Ghast right back out of your graveyard for just a single mana. As you sacrifice the Ghast to Yahenni, Undying Partisan to keep Yahenni protected and growing larger with +1/+1 counters, the Shambling Ghast's death ability triggers. Because Roaming Throne is on the battlefield declaring the correct creature type to double up triggers, that single sacrifice suddenly yields a double bounty of two Treasure tokens instead of one. Cracking those Treasures easily refunds the mana needed to fuel the Havengul Lich and cast the Ghast again, leaving you with an unstoppable cycle of sacrifices and endless resources.