The Extra Wildcard adds a blank tile to your Tile Bag. Blank tiles are not worth any points, but you can set them to any letter you want during an attack. At the start of Spelldom, your full Tile Bag will have 98 tiles, none of which are blank. There are 2 blank tiles available for purchase. Just like other tiles, they will come back when you refill your Tile Bag.
The Extra Discard allows you to replace your tiles more times during an attack. When your rack doesn't have any vowels or you need a certain letter for the win, discards are often the best and quickest solution. You start the game with 2 of them for each attack. You can unlock additional discards in the Special Store, up to a maximum of 5 per attack.
All Special Store purchases are permanent upgrades!