Legality depends on the tournament format -- Heartstone can be legal in some formats and banned or restricted in others
People were genuinely upset at the Windgrace deck, and I do understand why now
You may cast a spell from among them with mana value less than or equal to the greatest power among attacking creatures you control without paying its mana cost
This deck will not be able to beat the fastest lucky aggro decks, decks with a lot of haste, and likely some others, but at least you'll usually be able to not-die for a long time, that's kinda fun
Shadowheart, Dark Justiciar costs mana to use, but it can easily draw a lot more cards
Where it does shine is in its ability Taxes Should Hurt, which allows the player to deal one damage to a chosen opposing character whenever they discard a card