Shock would still deal 2 damage to Eager Construct, but this time that damage is being dealt before Titanic Growth can resolve and take effectso 2 damage is enough to destroy Eager Construct
Discover is a keyword action, so it resolves if the ability on the stack does, similar to scry, mill, and surveil, among others
The decklist above, piloted by Tulio Jaudy to a positive record at a recent Magic Online Challenge, focuses on rapidly filling the graveyard with cards like Fallaji Archaeologist and Overlord of the Balemurk
Rather, a second "reflexive" ability triggers when you sacrifice The Falcon this way
Kasla should help with that as the game goes along, and other cards in the deck like Skullclamp will help dig for cards