In this scenario Volcano Hellion reads, "Chose any number, Volcano Hellion deals twice that amount of damage to an opponent." Seriously, if we choose 10,000 with Volcano Hellion, we will deal 20,000 damage to our opponent
In the Ehren example above, the effect of Night Assailant is activating on the field and may still be negated by Shadow-Imprisoning Mirror
No matter if you searched your entire library or only some part of it (for instace being limited by the cunning opponents Aven Mindcensor), or even could not search at all (if your cunning opponent cast a Shadow of Doubt that resolved before your Gifts Ungiven), or you could but chose not to find anything, you have to shuffle your entire library anyways
In a similar way to the Archetype above, the Spirit of the Labyrinth suffers from Fragile Creature Syndrome
Imagine a Flames of the Firebrand or a Forked Bolt every turn, and better if you have bigger equipment