It fits well into a reanimator curve, especially if the following turn you play a card like The Cruelty of Gix
These will always detail how and when you use them, although it should be noted that many abilities for lower level characters will often exert the card which is symbolised with a small icon indicating a turning arrow
No, you don't have to, but the Smart Ass will be unblockable
The main way to get new cards in the game is to participate in in-game events
Treacherous Blessing + Demonic Lore Mainstays of decks that can sac them (like the uber annoying Doom Foretold decks), blink them, give them to opponents after the sweet cards are drawn, or all three, Treacherous Blessing and Demonic Lore can still get you three cards for 3 even if you cant do any of those, which is a great rate
For a detailed authentication process, see our fake detection guide