text: Streetwise Negotiator’s ability doesn’t actually change any creature’s power. It changes only the amount of combat damage the creature assigns. All other rules and effects that check power or toughness use the real values, even if they cause damage “equal to a creature’s power” to be dealt. Notably, if Streetwise Negotiator (or the creature that gains its ability) fights, it uses its actual power to determine how much damage it deals.