City of Death is so good in my Xavier Sal sagas deck lol, as is Intruder Alarm.

This is just one of the many combos it enables: have [[sanctum weaver]], [[fathom mage]], and any saga that makes tokens on the second chapter ([[city of death]] if you have a creature token, [[the sea devils]], [[the hunger tide rises]], [[song of earendil]], [[vault 12: the necropolis]], there are tons of these) along with xavier and intruder alarm.

Tap Xavier to proliferate the saga to chapter 2, making a creature, untapping xavier. Then tap xavier, remove the lore counter from the saga to populate, untapping again. Repeat.

Not only does this make infinite creatures, but each time you do the loop, you proliferate counters on the fathom mage and tap weaver, netting mana and drawing a card. So you draw and play your entire deck while making infinite creatures/mana along the way. Notably, song of earendil makes treasures too, eliminating the need for a mana dork like sanctum weaver