I've had an idea like this, only instead of the destruction caused, it was for the monsters themselves.
D1: The weakest of the weak, able to be harmed by hand held weapons. (Yog Trio)
D2: Monsters that are weak in the grand scheme of things, but are able to withstand more punishment than D1s. (Baragon)
D3: Monsters that can hold out against conventional weaponry, but can't cause tremendous amounts of damage before being driven off. (Varan, Anguirus)
D4: Monsters that can handle the majority of whatever's thrown at them. Can cause mass amounts of damage, but don't go out of their way to do so. (Godzilla, Rodan)
D5: Planet killers, the worst of the worst. Can really only be harmed and/or killed by other monsters. (King Ghidorah)
Today, at the edge of our hope...
At the end of our time, we have chosen to believe in each other.
Today we face the monsters that are at our door.
TODAY WE ARE CANCELLING THE APOCALYPSE!