Nullhide Ferox

A 6/6 with hexproof for four mana is a rate that has no business existing on a fair creature, so the design pays for it with a tax that cuts against everything green wants to do alongside a threat: a hard prohibition on casting noncreature spells while it sits in play. Your removal, your pump, your card draw, your ramp all go dark if they come off an instant, sorcery, artifact, or enchantment; you can still cast creatures, so a body-based shell keeps humming around it, which is precisely the deckbuilding puzzle it sets. The escape hatch strips the card's own text through end of turn, and the genuinely strange part is that any player may pay the two mana, so an opponent can switch off the prohibition (and the hexproof) on a turn that suits them, not you. That openness is the real tension: the ability is public, and the card dares both sides to time it. The discard clause guards the other exit. Hexproof stops opponents from targeting the creature with their spells and abilities, but nothing stops an opponent's discard effect from forcing it out of your hand; ordinarily that pitches it to the graveyard, but instead it deploys straight onto the battlefield, so the natural way to strip an unruly hexproof threat before it lands becomes a free way to hand it to you. The whole package is a study in conditional drawbacks: a body priced like a mistake, wrapped in a restriction its controller cannot fully control.