In Tempest, it was turn one (Mogg Fanatics, shadow creatures, and flyers), Invasion turn two (2/2 bears for every possible color combination plus several one- and two-mana apprentices and utility creatures), and Mirage turn three
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as an escape cost), add any cost increases, then apply any cost reductions
I decided I would pick one up at the GP before the event
Overload [cost] means "You may choose to pay [cost] rather than pay this spell's mana cost" and "If you chose to pay this spell's overload cost, change its text by replacing all instances of the word 'target' with the word 'each.'" If you don't pay the overload cost of a spell with overload, that spell will have a single target
Here's another common synergy - fetch lands
Its a black card with the Darkness logo in the center