Activate Tawnos' second ability by paying ({1} magic symbol) ({W} magic symbol) ({U} magic symbol) ({B} magic symbol) , sacrificing two artifact tokens, and exiling Priest of Gix from your graveyard, creating a token copy of Priest of Gix that is an artifact in addition to its other types.
The Priest of Gix token enters the battlefield, triggering itself and Intruder Alarm.
Resolve the Priest of Gix trigger, adding ({B} magic symbol) ({B} magic symbol) ({B} magic symbol) .
Resolve the Intruder Alarm trigger, untapping all creatures.
Activate Tawnos' first ability by paying ({2} magic symbol) and tapping it, creating a token copy of the Priest of Gix token, and causing you to mill two cards.
Repeat from step 2.
Once you have infinite black mana, you may instead choose any other artifact token(s) to make infinite copies of them.