Cards that help your attackers get through unblocked like Cyclonic Rift are essential for infect decks
That alone should be enough to get people to play him
Creature - Vampire Rogue Start the TARDIS Surveil 2, then draw a card
When playing with double-faced cards, either the traditional transforming ones or their shiny new modal cousins, it's important to that your cards are indistinguishable from one another
Arcane Proxy feels like less of a standout bomb than most of the cards on this list, but it's one of those build-arounds where you barely have to put effort in to make it good, and so 98 out of 98 players first picked it
In War of the Spark, you need to get +1/+1 counters onto your creatures (which usually involves using a spell like Battlefield Promotion or jumping through a hoop as with Makeshift Battalion) and then Proliferate to magnify those counters effect