The Superhero Database Classification number, or SHDB Class, is a number that represents the overall 'power' of a character. All traits of a character are used for calculating the Classification.
What it DOESN'T mean
This doesn't mean that a higher class would always beat a lower class character. But the bigger the difference in Class is, the more obvious it is who'll win in a fight.
How is this calculated
( INT^1.3 + (STR*0.5 )^2 + (SPE*0.5)^2 + DUR^1.6 + (POW + (SPS*SPL))^2 + COM^1.8 ) ^ TIER
Super Power Score and Level
Every Super Power has a score (SPS) that is used to calculate the Class. Each Super Power also has 3 levels (SPL). The level is set when connecting that Super Power to a character. The level determines the final score, of the Super Power, being used in the calculation.
Klaus can't kill Selene simply because she is far more powerful than he is.
The likely result for this match would be for both to survive but Klaus ends up without arms and legs and hanging from a metal chain hook full of bullet holes, unable to do anything but wiggle his now useless body for eternity.
Probably would also lack teeth and would have to eat through a straw.
Look at this, this way, it's a superhero that can't die but is a normal human vs superman, no matter how much he tried, he can't kill superman because he is far too powerful, but at the same time, you know superman can't kill the immortal dude, so what is going to happen there?