When Prosperous Innkeeper dies, Nim Deathmantle triggers, causing you to pay ({4} magic symbol) to return Prosperous Innkeeper from your graveyard to the battlefield, and attach Nim Deathmantle to it.
When Prosperous Innkeeper enters the battlefield, it triggers, creating two Treasure artifact tokens.
Activate the Treasures by tapping and sacrificing them, adding ({2} magic symbol) .