Hmm i have thought some more about level 20. Maybe you have to kill him with a spell/weapon which has the attack power equal to his health? (Like he has 3 health points left and you kill him with the shotgun which has 3 in attack power) I seriously don't know but as a tip i killed him with the shotgun when he had 3 health left, so I THINK you have to use either the Blast'em (shotgun), Tommy gun or the Raid card on him to finish him off when his health is low enough to kill him. Or it's compleatley random whatever kills him (like this game wasn't random and luck based enough).
Necronomiconquerer
Dude! You just completed the Necronomiconquerer achievement in The Necronomicon and won the Necronomiconquerer badge and 60 points!
YES! FINALLY! Man this game...i will never play this game again! Seriously, i was going nuts at challenge 20! M-A-N that was a hard one to figure out but now i think know how to do it. Use the shotgun when his health is low to kill him. I don't think the sanity level on him makes any diffrence (apart from the fact that you will win easier =)). Simple as that! (Ok it ain't simple but yeah... good luck anyway.)
Challenge mode is just a piece of shit based on luck where your opponent keeps on gettin the good cards and have the upper hand all the time. After i get the impossible bagde, i'll never play this game again!
 "The Necronomicon"){kind=icon}
 "Achilles"){kind=icon}
 "Dead Frontier Night Three"){kind=icon}