Monomania

Mind Twist taxes mana to empty a hand; this collapses it to a single card for a fixed five, and hands the victim the choice of which card survives. That choice is the whole design tension. The symmetric-looking generosity ("you get to keep one") is the cruelest kind of discard: against a hand of situational answers, leaving them one card means everything else goes regardless of what they wanted to keep. The flat cost separates it cleanly from scaling discard: you pay full freight whether they hold seven cards or two, which means the most devastating line is the obvious one. Cast it into a freshly drawn opening grip and a seven-card hand becomes a one-card hand for the same five mana, a swing no fixed-cost discard before it could match. Sorcery speed is the restriction that holds it back from oppression: it cannot strip a card off the top in response to a draw step, cannot react to anything, and only ever touches cards already resting in hand. So it works on two clocks at once. It can be the early haymaker that guts a full hand before the opponent has spent it, or the resource-denial play that lands once they have rebuilt to a few cards and lets you trade your card and five mana for all but one of theirs. Generous in framing, brutal in effect.