When Gandalf enters, it and Deadeye Navigator's soulbond ability trigger.
Resolve the Deadeye Navigator trigger, repairing it and Gandalf.
Resolve the Gandalf trigger, dealing 3 damage to Smaug.
Smaug triggers, creating three Treasure tokens.
Activate two Treasures by tapping and sacrificing them, adding 1.
Repeat.
This delightful loop turns Smaug the Impenetrable into a literal goldmine by exploiting the targeted damage from Gandalf, Spark Starter as it enters the battlefield. Thanks to Deadeye Navigator pairing up with Gandalf via soulbond, you have a repeatable blink engine right at your fingertips that continuously resets Gandalf's entry ability. Every time Gandalf drops back in to singe Smaug with 3 damage, Smaug the Impenetrable's triggered ability steps in to shower you with three shiny Treasure tokens. Sacrificing just two of those Treasures easily funds the {1}{U} blink cost to repeat the whole spectacle indefinitely, yielding an endless bounty of mana, triggers, and treasures.