I think there is one Level left untouched, one that is, quite creepily, the biggest-as-heck threat there is, but so far unknown of its appropiate usage since the few examples running through Coreline (and that have not been terminated on sight) are showing some kind of restraint (be it being kept out of the loop, CLULESS sawing off their potential power, or appropiate contermeasures (like the above-mentioned termination on sight) have been taken).
THREAT LEVEL 11-12: GALAXY/UNIVERSE DESTROYERS: Exactly what it says on the tin. Threats that wipe out entire *galaxies* and *universes* off the map. Threats that all the other Levels of Threat would actually unite to destroy-if they get lucky enough to win.
Examples include reality warpers like Haruhi Suzumiya and Anthony Fremont, several versions of the Gurren-Dan (which have mecha that can *step on galaxies*, as well as the infamous 'Spiral Nemesis Scenario' ) and the Anti-Spiral Group, the Anti-Life Equation, Krona (at full power), the C'Tan (and, arguably, the Old Chaos Gods and the Neo-Chaos), et al.
While we're at it... where would Cthulhu be, then? On Level 10?