Sudden Strike

The condition on this removal is not a downside the deck-builder chooses to accept: it is the whole design philosophy of white's "fair" removal in two words. White does not get to point at any creature and kill it the way black does; it gets to kill things that have committed to combat. The attacking-or-blocking clause turns the spell into a pure reactive tool, useless on the mana dork sitting quietly and lethal on the giant swinging in. That timing wrinkle is where the value lives: fired off once attackers are declared, it removes a threat before damage while leaving your own board free to block, and held for the opponent's block step, it can ambush a creature that thought it was safely trading. It descends from white's tradition of combat-locked kill spells, the effect that lets the color have unconditional destruction only inside the phase where white is supposed to be strong. What it cannot do is answer a problem permanent on a turn nobody is attacking, and that gap is exactly the price white pays for getting clean two-mana destruction at all.