The Darkness Crystal is fine and might actually be a funny sideboard card against the sacrifice decks because it turns off death triggers, but its usually not worth the mana investment
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This eight-mana 7/5 Juggernaut turns all your creatures into Juggernauts too, setting their power and toughness to 5/3 and forcing them to attack every turn, but also making it so they can't be blocked by Wall creatures, making that one Wall player in your group look real awkward in a match
All it needs to do is land a hit on an opponent, but since it only costs two mana, you can probably sneak out a couple higher-cost Goblins early, before one of your opponents gets defenders in place