Demoralize

Falter effects live or die by their ceiling, and this one builds a second gear into the cost. The base mode hands every creature menace, which is the polite version of the trick: your attackers each need a pair of blockers to be stopped rather than one, which thins what an opponent can profitably gang up on. The symmetry is harmless when you cast it on your own turn to attack, because the effect lasts only until end of turn; the opponent's creatures gain menace while they are defending, which does nothing for them. So there is no real downside to the floor, just a question of whether menace alone is enough. Get seven or more cards into the graveyard and the spell stops negotiating: blockers vanish entirely for the turn, the full Falter, no caveats. That escalation is the design idea. A vanilla "creatures can't block" instant is a known quantity aggressive red decks have always wanted; gating the strongest version behind threshold lets the card cost what a half-measure should cost while still delivering the kill once the game has run long enough to deserve it. The whole question the card poses is one of timing rather than construction: hold it while the graveyard fills, and you trade a turn of patience for the difference between "harder to block" and "unblockable." It is a finisher disguised as a combat trick, and the line between the two is exactly seven cards deep.